unofficial mirror of emacs-devel@gnu.org 
 help / color / mirror / code / Atom feed
blob 2e7c497f5774ca66eae1d94feeed26b1c82a9c7e 233745 bytes (raw)
name: doc/lispref/text.texi 	 # note: path name is non-authoritative(*)

   1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116
 117
 118
 119
 120
 121
 122
 123
 124
 125
 126
 127
 128
 129
 130
 131
 132
 133
 134
 135
 136
 137
 138
 139
 140
 141
 142
 143
 144
 145
 146
 147
 148
 149
 150
 151
 152
 153
 154
 155
 156
 157
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167
 168
 169
 170
 171
 172
 173
 174
 175
 176
 177
 178
 179
 180
 181
 182
 183
 184
 185
 186
 187
 188
 189
 190
 191
 192
 193
 194
 195
 196
 197
 198
 199
 200
 201
 202
 203
 204
 205
 206
 207
 208
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222
 223
 224
 225
 226
 227
 228
 229
 230
 231
 232
 233
 234
 235
 236
 237
 238
 239
 240
 241
 242
 243
 244
 245
 246
 247
 248
 249
 250
 251
 252
 253
 254
 255
 256
 257
 258
 259
 260
 261
 262
 263
 264
 265
 266
 267
 268
 269
 270
 271
 272
 273
 274
 275
 276
 277
 278
 279
 280
 281
 282
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293
 294
 295
 296
 297
 298
 299
 300
 301
 302
 303
 304
 305
 306
 307
 308
 309
 310
 311
 312
 313
 314
 315
 316
 317
 318
 319
 320
 321
 322
 323
 324
 325
 326
 327
 328
 329
 330
 331
 332
 333
 334
 335
 336
 337
 338
 339
 340
 341
 342
 343
 344
 345
 346
 347
 348
 349
 350
 351
 352
 353
 354
 355
 356
 357
 358
 359
 360
 361
 362
 363
 364
 365
 366
 367
 368
 369
 370
 371
 372
 373
 374
 375
 376
 377
 378
 379
 380
 381
 382
 383
 384
 385
 386
 387
 388
 389
 390
 391
 392
 393
 394
 395
 396
 397
 398
 399
 400
 401
 402
 403
 404
 405
 406
 407
 408
 409
 410
 411
 412
 413
 414
 415
 416
 417
 418
 419
 420
 421
 422
 423
 424
 425
 426
 427
 428
 429
 430
 431
 432
 433
 434
 435
 436
 437
 438
 439
 440
 441
 442
 443
 444
 445
 446
 447
 448
 449
 450
 451
 452
 453
 454
 455
 456
 457
 458
 459
 460
 461
 462
 463
 464
 465
 466
 467
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486
 487
 488
 489
 490
 491
 492
 493
 494
 495
 496
 497
 498
 499
 500
 501
 502
 503
 504
 505
 506
 507
 508
 509
 510
 511
 512
 513
 514
 515
 516
 517
 518
 519
 520
 521
 522
 523
 524
 525
 526
 527
 528
 529
 530
 531
 532
 533
 534
 535
 536
 537
 538
 539
 540
 541
 542
 543
 544
 545
 546
 547
 548
 549
 550
 551
 552
 553
 554
 555
 556
 557
 558
 559
 560
 561
 562
 563
 564
 565
 566
 567
 568
 569
 570
 571
 572
 573
 574
 575
 576
 577
 578
 579
 580
 581
 582
 583
 584
 585
 586
 587
 588
 589
 590
 591
 592
 593
 594
 595
 596
 597
 598
 599
 600
 601
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
3694
3695
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
3740
3741
3742
3743
3744
3745
3746
3747
3748
3749
3750
3751
3752
3753
3754
3755
3756
3757
3758
3759
3760
3761
3762
3763
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
3779
3780
3781
3782
3783
3784
3785
3786
3787
3788
3789
3790
3791
3792
3793
3794
3795
3796
3797
3798
3799
3800
3801
3802
3803
3804
3805
3806
3807
3808
3809
3810
3811
3812
3813
3814
3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
3829
3830
3831
3832
3833
3834
3835
3836
3837
3838
3839
3840
3841
3842
3843
3844
3845
3846
3847
3848
3849
3850
3851
3852
3853
3854
3855
3856
3857
3858
3859
3860
3861
3862
3863
3864
3865
3866
3867
3868
3869
3870
3871
3872
3873
3874
3875
3876
3877
3878
3879
3880
3881
3882
3883
3884
3885
3886
3887
3888
3889
3890
3891
3892
3893
3894
3895
3896
3897
3898
3899
3900
3901
3902
3903
3904
3905
3906
3907
3908
3909
3910
3911
3912
3913
3914
3915
3916
3917
3918
3919
3920
3921
3922
3923
3924
3925
3926
3927
3928
3929
3930
3931
3932
3933
3934
3935
3936
3937
3938
3939
3940
3941
3942
3943
3944
3945
3946
3947
3948
3949
3950
3951
3952
3953
3954
3955
3956
3957
3958
3959
3960
3961
3962
3963
3964
3965
3966
3967
3968
3969
3970
3971
3972
3973
3974
3975
3976
3977
3978
3979
3980
3981
3982
3983
3984
3985
3986
3987
3988
3989
3990
3991
3992
3993
3994
3995
3996
3997
3998
3999
4000
4001
4002
4003
4004
4005
4006
4007
4008
4009
4010
4011
4012
4013
4014
4015
4016
4017
4018
4019
4020
4021
4022
4023
4024
4025
4026
4027
4028
4029
4030
4031
4032
4033
4034
4035
4036
4037
4038
4039
4040
4041
4042
4043
4044
4045
4046
4047
4048
4049
4050
4051
4052
4053
4054
4055
4056
4057
4058
4059
4060
4061
4062
4063
4064
4065
4066
4067
4068
4069
4070
4071
4072
4073
4074
4075
4076
4077
4078
4079
4080
4081
4082
4083
4084
4085
4086
4087
4088
4089
4090
4091
4092
4093
4094
4095
4096
4097
4098
4099
4100
4101
4102
4103
4104
4105
4106
4107
4108
4109
4110
4111
4112
4113
4114
4115
4116
4117
4118
4119
4120
4121
4122
4123
4124
4125
4126
4127
4128
4129
4130
4131
4132
4133
4134
4135
4136
4137
4138
4139
4140
4141
4142
4143
4144
4145
4146
4147
4148
4149
4150
4151
4152
4153
4154
4155
4156
4157
4158
4159
4160
4161
4162
4163
4164
4165
4166
4167
4168
4169
4170
4171
4172
4173
4174
4175
4176
4177
4178
4179
4180
4181
4182
4183
4184
4185
4186
4187
4188
4189
4190
4191
4192
4193
4194
4195
4196
4197
4198
4199
4200
4201
4202
4203
4204
4205
4206
4207
4208
4209
4210
4211
4212
4213
4214
4215
4216
4217
4218
4219
4220
4221
4222
4223
4224
4225
4226
4227
4228
4229
4230
4231
4232
4233
4234
4235
4236
4237
4238
4239
4240
4241
4242
4243
4244
4245
4246
4247
4248
4249
4250
4251
4252
4253
4254
4255
4256
4257
4258
4259
4260
4261
4262
4263
4264
4265
4266
4267
4268
4269
4270
4271
4272
4273
4274
4275
4276
4277
4278
4279
4280
4281
4282
4283
4284
4285
4286
4287
4288
4289
4290
4291
4292
4293
4294
4295
4296
4297
4298
4299
4300
4301
4302
4303
4304
4305
4306
4307
4308
4309
4310
4311
4312
4313
4314
4315
4316
4317
4318
4319
4320
4321
4322
4323
4324
4325
4326
4327
4328
4329
4330
4331
4332
4333
4334
4335
4336
4337
4338
4339
4340
4341
4342
4343
4344
4345
4346
4347
4348
4349
4350
4351
4352
4353
4354
4355
4356
4357
4358
4359
4360
4361
4362
4363
4364
4365
4366
4367
4368
4369
4370
4371
4372
4373
4374
4375
4376
4377
4378
4379
4380
4381
4382
4383
4384
4385
4386
4387
4388
4389
4390
4391
4392
4393
4394
4395
4396
4397
4398
4399
4400
4401
4402
4403
4404
4405
4406
4407
4408
4409
4410
4411
4412
4413
4414
4415
4416
4417
4418
4419
4420
4421
4422
4423
4424
4425
4426
4427
4428
4429
4430
4431
4432
4433
4434
4435
4436
4437
4438
4439
4440
4441
4442
4443
4444
4445
4446
4447
4448
4449
4450
4451
4452
4453
4454
4455
4456
4457
4458
4459
4460
4461
4462
4463
4464
4465
4466
4467
4468
4469
4470
4471
4472
4473
4474
4475
4476
4477
4478
4479
4480
4481
4482
4483
4484
4485
4486
4487
4488
4489
4490
4491
4492
4493
4494
4495
4496
4497
4498
4499
4500
4501
4502
4503
4504
4505
4506
4507
4508
4509
4510
4511
4512
4513
4514
4515
4516
4517
4518
4519
4520
4521
4522
4523
4524
4525
4526
4527
4528
4529
4530
4531
4532
4533
4534
4535
4536
4537
4538
4539
4540
4541
4542
4543
4544
4545
4546
4547
4548
4549
4550
4551
4552
4553
4554
4555
4556
4557
4558
4559
4560
4561
4562
4563
4564
4565
4566
4567
4568
4569
4570
4571
4572
4573
4574
4575
4576
4577
4578
4579
4580
4581
4582
4583
4584
4585
4586
4587
4588
4589
4590
4591
4592
4593
4594
4595
4596
4597
4598
4599
4600
4601
4602
4603
4604
4605
4606
4607
4608
4609
4610
4611
4612
4613
4614
4615
4616
4617
4618
4619
4620
4621
4622
4623
4624
4625
4626
4627
4628
4629
4630
4631
4632
4633
4634
4635
4636
4637
4638
4639
4640
4641
4642
4643
4644
4645
4646
4647
4648
4649
4650
4651
4652
4653
4654
4655
4656
4657
4658
4659
4660
4661
4662
4663
4664
4665
4666
4667
4668
4669
4670
4671
4672
4673
4674
4675
4676
4677
4678
4679
4680
4681
4682
4683
4684
4685
4686
4687
4688
4689
4690
4691
4692
4693
4694
4695
4696
4697
4698
4699
4700
4701
4702
4703
4704
4705
4706
4707
4708
4709
4710
4711
4712
4713
4714
4715
4716
4717
4718
4719
4720
4721
4722
4723
4724
4725
4726
4727
4728
4729
4730
4731
4732
4733
4734
4735
4736
4737
4738
4739
4740
4741
4742
4743
4744
4745
4746
4747
4748
4749
4750
4751
4752
4753
4754
4755
4756
4757
4758
4759
4760
4761
4762
4763
4764
4765
4766
4767
4768
4769
4770
4771
4772
4773
4774
4775
4776
4777
4778
4779
4780
4781
4782
4783
4784
4785
4786
4787
4788
4789
4790
4791
4792
4793
4794
4795
4796
4797
4798
4799
4800
4801
4802
4803
4804
4805
4806
4807
4808
4809
4810
4811
4812
4813
4814
4815
4816
4817
4818
4819
4820
4821
4822
4823
4824
4825
4826
4827
4828
4829
4830
4831
4832
4833
4834
4835
4836
4837
4838
4839
4840
4841
4842
4843
4844
4845
4846
4847
4848
4849
4850
4851
4852
4853
4854
4855
4856
4857
4858
4859
4860
4861
4862
4863
4864
4865
4866
4867
4868
4869
4870
4871
4872
4873
4874
4875
4876
4877
4878
4879
4880
4881
4882
4883
4884
4885
4886
4887
4888
4889
4890
4891
4892
4893
4894
4895
4896
4897
4898
4899
4900
4901
4902
4903
4904
4905
4906
4907
4908
4909
4910
4911
4912
4913
4914
4915
4916
4917
4918
4919
4920
4921
4922
4923
4924
4925
4926
4927
4928
4929
4930
4931
4932
4933
4934
4935
4936
4937
4938
4939
4940
4941
4942
4943
4944
4945
4946
4947
4948
4949
4950
4951
4952
4953
4954
4955
4956
4957
4958
4959
4960
4961
4962
4963
4964
4965
4966
4967
4968
4969
4970
4971
4972
4973
4974
4975
4976
4977
4978
4979
4980
4981
4982
4983
4984
4985
4986
4987
4988
4989
4990
4991
4992
4993
4994
4995
4996
4997
4998
4999
5000
5001
5002
5003
5004
5005
5006
5007
5008
5009
5010
5011
5012
5013
5014
5015
5016
5017
5018
5019
5020
5021
5022
5023
5024
5025
5026
5027
5028
5029
5030
5031
5032
5033
5034
5035
5036
5037
5038
5039
5040
5041
5042
5043
5044
5045
5046
5047
5048
5049
5050
5051
5052
5053
5054
5055
5056
5057
5058
5059
5060
5061
5062
5063
5064
5065
5066
5067
5068
5069
5070
5071
5072
5073
5074
5075
5076
5077
5078
5079
5080
5081
5082
5083
5084
5085
5086
5087
5088
5089
5090
5091
5092
5093
5094
5095
5096
5097
5098
5099
5100
5101
5102
5103
5104
5105
5106
5107
5108
5109
5110
5111
5112
5113
5114
5115
5116
5117
5118
5119
5120
5121
5122
5123
5124
5125
5126
5127
5128
5129
5130
5131
5132
5133
5134
5135
5136
5137
5138
5139
5140
5141
5142
5143
5144
5145
5146
5147
5148
5149
5150
5151
5152
5153
5154
5155
5156
5157
5158
5159
5160
5161
5162
5163
5164
5165
5166
5167
5168
5169
5170
5171
5172
5173
5174
5175
5176
5177
5178
5179
5180
5181
5182
5183
5184
5185
5186
5187
5188
5189
5190
5191
5192
5193
5194
5195
5196
5197
5198
5199
5200
5201
5202
5203
5204
5205
5206
5207
5208
5209
5210
5211
5212
5213
5214
5215
5216
5217
5218
5219
5220
5221
5222
5223
5224
5225
5226
5227
5228
5229
5230
5231
5232
5233
5234
5235
5236
5237
5238
5239
5240
5241
5242
5243
5244
5245
5246
5247
5248
5249
5250
5251
5252
5253
5254
5255
5256
5257
5258
5259
5260
5261
5262
5263
5264
5265
5266
5267
5268
5269
5270
5271
5272
5273
5274
5275
5276
5277
5278
5279
5280
5281
5282
5283
5284
5285
5286
5287
5288
5289
5290
5291
5292
5293
5294
5295
5296
5297
5298
5299
5300
5301
5302
5303
5304
5305
5306
5307
5308
5309
5310
5311
5312
5313
5314
5315
5316
5317
5318
5319
5320
5321
5322
5323
5324
5325
5326
5327
5328
5329
5330
5331
5332
5333
5334
5335
5336
5337
5338
5339
5340
5341
5342
5343
5344
5345
5346
5347
5348
5349
5350
5351
5352
5353
5354
5355
5356
5357
5358
5359
5360
5361
5362
5363
5364
5365
5366
5367
5368
5369
5370
5371
5372
5373
5374
5375
5376
5377
5378
5379
5380
5381
5382
5383
5384
5385
5386
5387
5388
5389
5390
5391
5392
5393
5394
5395
5396
5397
5398
5399
5400
5401
5402
5403
5404
5405
5406
5407
5408
5409
5410
5411
5412
5413
5414
5415
5416
5417
5418
5419
5420
5421
5422
5423
5424
5425
5426
5427
5428
5429
5430
5431
5432
5433
5434
5435
5436
5437
5438
5439
5440
5441
5442
5443
5444
5445
5446
5447
5448
5449
5450
5451
5452
5453
5454
5455
5456
5457
5458
5459
5460
5461
5462
5463
5464
5465
5466
5467
5468
5469
5470
5471
5472
5473
5474
5475
5476
5477
5478
5479
5480
5481
5482
5483
5484
5485
5486
5487
5488
5489
5490
5491
5492
5493
5494
5495
5496
5497
5498
5499
5500
5501
5502
5503
5504
5505
5506
5507
5508
5509
5510
5511
5512
5513
5514
5515
5516
5517
5518
5519
5520
5521
5522
5523
5524
5525
5526
5527
5528
5529
5530
5531
5532
5533
5534
5535
5536
5537
5538
5539
5540
5541
5542
5543
5544
5545
5546
5547
5548
5549
5550
5551
5552
5553
5554
5555
5556
5557
5558
5559
5560
5561
5562
5563
5564
5565
5566
5567
5568
5569
5570
5571
5572
5573
5574
5575
5576
5577
5578
5579
5580
5581
5582
5583
5584
5585
5586
5587
5588
5589
5590
5591
5592
5593
5594
5595
5596
5597
5598
5599
5600
5601
5602
5603
5604
5605
5606
5607
5608
5609
5610
5611
5612
5613
5614
5615
5616
5617
5618
5619
5620
5621
5622
5623
5624
5625
5626
5627
5628
5629
5630
5631
5632
5633
5634
5635
5636
5637
5638
5639
5640
5641
5642
5643
5644
5645
5646
5647
5648
5649
5650
5651
5652
5653
5654
 
@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
@c Copyright (C) 1990-1995, 1998-2019 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@node Text
@chapter Text
@cindex text

  This chapter describes the functions that deal with the text in a
buffer.  Most examine, insert, or delete text in the current buffer,
often operating at point or on text adjacent to point.  Many are
interactive.  All the functions that change the text provide for undoing
the changes (@pxref{Undo}).

  Many text-related functions operate on a region of text defined by two
buffer positions passed in arguments named @var{start} and @var{end}.
These arguments should be either markers (@pxref{Markers}) or numeric
character positions (@pxref{Positions}).  The order of these arguments
does not matter; it is all right for @var{start} to be the end of the
region and @var{end} the beginning.  For example, @code{(delete-region 1
10)} and @code{(delete-region 10 1)} are equivalent.  An
@code{args-out-of-range} error is signaled if either @var{start} or
@var{end} is outside the accessible portion of the buffer.  In an
interactive call, point and the mark are used for these arguments.

@cindex buffer contents
  Throughout this chapter, ``text'' refers to the characters in the
buffer, together with their properties (when relevant).  Keep in mind
that point is always between two characters, and the cursor appears on
the character after point.

@menu
* Near Point::       Examining text in the vicinity of point.
* Buffer Contents::  Examining text in a general fashion.
* Comparing Text::   Comparing substrings of buffers.
* Insertion::        Adding new text to a buffer.
* Commands for Insertion::  User-level commands to insert text.
* Deletion::         Removing text from a buffer.
* User-Level Deletion::     User-level commands to delete text.
* The Kill Ring::    Where removed text sometimes is saved for later use.
* Undo::             Undoing changes to the text of a buffer.
* Maintaining Undo:: How to enable and disable undo information.
                        How to control how much information is kept.
* Filling::          Functions for explicit filling.
* Margins::          How to specify margins for filling commands.
* Adaptive Fill::    Adaptive Fill mode chooses a fill prefix from context.
* Auto Filling::     How auto-fill mode is implemented to break lines.
* Sorting::          Functions for sorting parts of the buffer.
* Columns::          Computing horizontal positions, and using them.
* Indentation::      Functions to insert or adjust indentation.
* Case Changes::     Case conversion of parts of the buffer.
* Text Properties::  Assigning Lisp property lists to text characters.
* Substitution::     Replacing a given character wherever it appears.
* Registers::        How registers are implemented.  Accessing the text or
                       position stored in a register.
* Transposition::    Swapping two portions of a buffer.
* Replacing::        Replacing the text of one buffer with the text
                       of another buffer.
* Decompression::    Dealing with compressed data.
* Base 64::          Conversion to or from base 64 encoding.
* Checksum/Hash::    Computing cryptographic hashes.
* GnuTLS Cryptography:: Cryptographic algorithms imported from GnuTLS.
* Parsing HTML/XML:: Parsing HTML and XML.
* Parsing JSON::     Parsing and generating JSON values.
* JSONRPC::          JSON Remote Procedure Call protocol
* Atomic Changes::   Installing several buffer changes atomically.
* Change Hooks::     Supplying functions to be run when text is changed.
@end menu

@node Near Point
@section Examining Text Near Point
@cindex text near point

  Many functions are provided to look at the characters around point.
Several simple functions are described here.  See also @code{looking-at}
in @ref{Regexp Search}.

In the following four functions, ``beginning'' or ``end'' of buffer
refers to the beginning or end of the accessible portion.

@defun char-after &optional position
This function returns the character in the current buffer at (i.e.,
immediately after) position @var{position}.  If @var{position} is out of
range for this purpose, either before the beginning of the buffer, or at
or beyond the end, then the value is @code{nil}.  The default for
@var{position} is point.

In the following example, assume that the first character in the
buffer is @samp{@@}:

@example
@group
(string (char-after 1))
     @result{} "@@"
@end group
@end example
@end defun

@defun char-before &optional position
This function returns the character in the current buffer immediately
before position @var{position}.  If @var{position} is out of range for
this purpose, either at or before the beginning of the buffer, or beyond
the end, then the value is @code{nil}.  The default for
@var{position} is point.
@end defun

@defun following-char
This function returns the character following point in the current
buffer.  This is similar to @code{(char-after (point))}.  However, if
point is at the end of the buffer, then @code{following-char} returns 0.

Remember that point is always between characters, and the cursor
normally appears over the character following point.  Therefore, the
character returned by @code{following-char} is the character the
cursor is over.

In this example, point is between the @samp{a} and the @samp{c}.

@example
@group
---------- Buffer: foo ----------
Gentlemen may cry ``Pea@point{}ce! Peace!,''
but there is no peace.
---------- Buffer: foo ----------
@end group

@group
(string (preceding-char))
     @result{} "a"
(string (following-char))
     @result{} "c"
@end group
@end example
@end defun

@defun preceding-char
This function returns the character preceding point in the current
buffer.  See above, under @code{following-char}, for an example.  If
point is at the beginning of the buffer, @code{preceding-char} returns
0.
@end defun

@defun bobp
This function returns @code{t} if point is at the beginning of the
buffer.  If narrowing is in effect, this means the beginning of the
accessible portion of the text.  See also @code{point-min} in
@ref{Point}.
@end defun

@defun eobp
This function returns @code{t} if point is at the end of the buffer.
If narrowing is in effect, this means the end of accessible portion of
the text.  See also @code{point-max} in @xref{Point}.
@end defun

@defun bolp
This function returns @code{t} if point is at the beginning of a line.
@xref{Text Lines}.  The beginning of the buffer (or of its accessible
portion) always counts as the beginning of a line.
@end defun

@defun eolp
This function returns @code{t} if point is at the end of a line.  The
end of the buffer (or of its accessible portion) is always considered
the end of a line.
@end defun

@node Buffer Contents
@section Examining Buffer Contents
@cindex buffer portion as string

  This section describes functions that allow a Lisp program to
convert any portion of the text in the buffer into a string.

@defun buffer-substring start end
This function returns a string containing a copy of the text of the
region defined by positions @var{start} and @var{end} in the current
buffer.  If the arguments are not positions in the accessible portion
of the buffer, @code{buffer-substring} signals an
@code{args-out-of-range} error.

Here's an example which assumes Font-Lock mode is not enabled:

@example
@group
---------- Buffer: foo ----------
This is the contents of buffer foo

---------- Buffer: foo ----------
@end group

@group
(buffer-substring 1 10)
     @result{} "This is t"
@end group
@group
(buffer-substring (point-max) 10)
     @result{} "he contents of buffer foo\n"
@end group
@end example

If the text being copied has any text properties, these are copied into
the string along with the characters they belong to.  @xref{Text
Properties}.  However, overlays (@pxref{Overlays}) in the buffer and
their properties are ignored, not copied.

For example, if Font-Lock mode is enabled, you might get results like
these:

@example
@group
(buffer-substring 1 10)
     @result{} #("This is t" 0 1 (fontified t) 1 9 (fontified t))
@end group
@end example
@end defun

@defun buffer-substring-no-properties start end
This is like @code{buffer-substring}, except that it does not copy text
properties, just the characters themselves.  @xref{Text Properties}.
@end defun

@defun buffer-string
This function returns the contents of the entire accessible portion of
the current buffer, as a string.
@end defun

  If you need to make sure the resulting string, when copied to a
different location, will not change its visual appearance due to
reordering of bidirectional text, use the
@code{buffer-substring-with-bidi-context} function
(@pxref{Bidirectional Display, buffer-substring-with-bidi-context}).

@defun filter-buffer-substring start end &optional delete
This function filters the buffer text between @var{start} and @var{end}
using a function specified by the variable
@code{filter-buffer-substring-function}, and returns the result.

The default filter function consults the obsolete wrapper hook
@code{filter-buffer-substring-functions} (see the documentation string
of the macro @code{with-wrapper-hook} for the details about this
obsolete facility), and the obsolete variable
@code{buffer-substring-filters}.  If both of these are @code{nil}, it
returns the unaltered text from the buffer, i.e., what
@code{buffer-substring} would return.

If @var{delete} is non-@code{nil}, the function deletes the text
between @var{start} and @var{end} after copying it, like
@code{delete-and-extract-region}.

Lisp code should use this function instead of @code{buffer-substring},
@code{buffer-substring-no-properties},
or @code{delete-and-extract-region} when copying into user-accessible
data structures such as the kill-ring, X clipboard, and registers.
Major and minor modes can modify @code{filter-buffer-substring-function}
to alter such text as it is copied out of the buffer.
@end defun

@defvar filter-buffer-substring-function
The value of this variable is a function that @code{filter-buffer-substring}
will call to do the actual work.  The function receives three
arguments, the same as those of @code{filter-buffer-substring},
which it should treat as per the documentation of that function.  It
should return the filtered text (and optionally delete the source text).
@end defvar

@noindent The following two variables are obsoleted by
@code{filter-buffer-substring-function}, but are still supported for
backward compatibility.

@defvar filter-buffer-substring-functions
This obsolete variable is a wrapper hook, whose members should be functions
that accept four arguments: @var{fun}, @var{start}, @var{end}, and
@var{delete}.  @var{fun} is a function that takes three arguments
(@var{start}, @var{end}, and @var{delete}), and returns a string.  In
both cases, the @var{start}, @var{end}, and @var{delete} arguments are
the same as those of @code{filter-buffer-substring}.

The first hook function is passed a @var{fun} that is equivalent to
the default operation of @code{filter-buffer-substring}, i.e., it
returns the buffer-substring between @var{start} and @var{end}
(processed by any @code{buffer-substring-filters}) and optionally
deletes the original text from the buffer.  In most cases, the hook
function will call @var{fun} once, and then do its own processing of
the result.  The next hook function receives a @var{fun} equivalent to
this, and so on.  The actual return value is the result of all the
hook functions acting in sequence.
@end defvar

@defvar buffer-substring-filters
The value of this obsolete variable should be a list of functions
that accept a single string argument and return another string.
The default @code{filter-buffer-substring} function passes the buffer
substring to the first function in this list, and the return value of
each function is passed to the next function.  The return value of the
last function is passed to @code{filter-buffer-substring-functions}.
@end defvar

@defun current-word &optional strict really-word
This function returns the symbol (or word) at or near point, as a
string.  The return value includes no text properties.

If the optional argument @var{really-word} is non-@code{nil}, it finds a
word; otherwise, it finds a symbol (which includes both word
characters and symbol constituent characters).

If the optional argument @var{strict} is non-@code{nil}, then point
must be in or next to the symbol or word---if no symbol or word is
there, the function returns @code{nil}.  Otherwise, a nearby symbol or
word on the same line is acceptable.
@end defun

@defun thing-at-point thing &optional no-properties
Return the @var{thing} around or next to point, as a string.

The argument @var{thing} is a symbol which specifies a kind of syntactic
entity.  Possibilities include @code{symbol}, @code{list}, @code{sexp},
@code{defun}, @code{filename}, @code{url}, @code{word}, @code{sentence},
@code{whitespace}, @code{line}, @code{page}, and others.

When the optional argument @var{no-properties} is non-@code{nil}, this
function strips text properties from the return value.

@example
---------- Buffer: foo ----------
Gentlemen may cry ``Pea@point{}ce! Peace!,''
but there is no peace.
---------- Buffer: foo ----------

(thing-at-point 'word)
     @result{} "Peace"
(thing-at-point 'line)
     @result{} "Gentlemen may cry ``Peace! Peace!,''\n"
(thing-at-point 'whitespace)
     @result{} nil
@end example
@end defun

@node Comparing Text
@section Comparing Text
@cindex comparing buffer text

  This function lets you compare portions of the text in a buffer, without
copying them into strings first.

@defun compare-buffer-substrings buffer1 start1 end1 buffer2 start2 end2
This function lets you compare two substrings of the same buffer or two
different buffers.  The first three arguments specify one substring,
giving a buffer (or a buffer name) and two positions within the
buffer.  The last three arguments specify the other substring in the
same way.  You can use @code{nil} for @var{buffer1}, @var{buffer2}, or
both to stand for the current buffer.

The value is negative if the first substring is less, positive if the
first is greater, and zero if they are equal.  The absolute value of
the result is one plus the index of the first differing characters
within the substrings.

This function ignores case when comparing characters
if @code{case-fold-search} is non-@code{nil}.  It always ignores
text properties.

Suppose you have the text @w{@samp{foobarbar haha!rara!}} in the
current buffer; then in this example the two substrings are @samp{rbar
} and @samp{rara!}.  The value is 2 because the first substring is
greater at the second character.

@example
(compare-buffer-substrings nil 6 11 nil 16 21)
     @result{} 2
@end example
@end defun

@node Insertion
@section Inserting Text
@cindex insertion of text
@cindex text insertion

@cindex insertion before point
@cindex before point, insertion
  @dfn{Insertion} means adding new text to a buffer.  The inserted text
goes at point---between the character before point and the character
after point.  Some insertion functions leave point before the inserted
text, while other functions leave it after.  We call the former
insertion @dfn{after point} and the latter insertion @dfn{before point}.

  Insertion moves markers located at positions after the insertion
point, so that they stay with the surrounding text (@pxref{Markers}).
When a marker points at the place of insertion, insertion may or may
not relocate the marker, depending on the marker's insertion type
(@pxref{Marker Insertion Types}).  Certain special functions such as
@code{insert-before-markers} relocate all such markers to point after
the inserted text, regardless of the markers' insertion type.

  Insertion functions signal an error if the current buffer is
read-only (@pxref{Read Only Buffers}) or if they insert within
read-only text (@pxref{Special Properties}).

  These functions copy text characters from strings and buffers along
with their properties.  The inserted characters have exactly the same
properties as the characters they were copied from.  By contrast,
characters specified as separate arguments, not part of a string or
buffer, inherit their text properties from the neighboring text.

  The insertion functions convert text from unibyte to multibyte in
order to insert in a multibyte buffer, and vice versa---if the text
comes from a string or from a buffer.  However, they do not convert
unibyte character codes 128 through 255 to multibyte characters, not
even if the current buffer is a multibyte buffer.  @xref{Converting
Representations}.

@defun insert &rest args
This function inserts the strings and/or characters @var{args} into the
current buffer, at point, moving point forward.  In other words, it
inserts the text before point.  An error is signaled unless all
@var{args} are either strings or characters.  The value is @code{nil}.
@end defun

@defun insert-before-markers &rest args
This function inserts the strings and/or characters @var{args} into the
current buffer, at point, moving point forward.  An error is signaled
unless all @var{args} are either strings or characters.  The value is
@code{nil}.

This function is unlike the other insertion functions in that it
relocates markers initially pointing at the insertion point, to point
after the inserted text.  If an overlay begins at the insertion point,
the inserted text falls outside the overlay; if a nonempty overlay
ends at the insertion point, the inserted text falls inside that
overlay.
@end defun

@deffn Command insert-char character &optional count inherit
This command inserts @var{count} instances of @var{character} into the
current buffer before point.  The argument @var{count} must be an
integer, and @var{character} must be a character.

If called interactively, this command prompts for @var{character}
using its Unicode name or its code point.  @xref{Inserting Text,,,
emacs, The GNU Emacs Manual}.

This function does not convert unibyte character codes 128 through 255
to multibyte characters, not even if the current buffer is a multibyte
buffer.  @xref{Converting Representations}.

If @var{inherit} is non-@code{nil}, the inserted characters inherit
sticky text properties from the two characters before and after the
insertion point.  @xref{Sticky Properties}.
@end deffn

@defun insert-buffer-substring from-buffer-or-name &optional start end
This function inserts a portion of buffer @var{from-buffer-or-name}
into the current buffer before point.  The text inserted is the region
between @var{start} (inclusive) and @var{end} (exclusive).  (These
arguments default to the beginning and end of the accessible portion
of that buffer.)  This function returns @code{nil}.

In this example, the form is executed with buffer @samp{bar} as the
current buffer.  We assume that buffer @samp{bar} is initially empty.

@example
@group
---------- Buffer: foo ----------
We hold these truths to be self-evident, that all
---------- Buffer: foo ----------
@end group

@group
(insert-buffer-substring "foo" 1 20)
     @result{} nil

---------- Buffer: bar ----------
We hold these truth@point{}
---------- Buffer: bar ----------
@end group
@end example
@end defun

@defun insert-buffer-substring-no-properties from-buffer-or-name &optional start end
This is like @code{insert-buffer-substring} except that it does not
copy any text properties.
@end defun

  @xref{Sticky Properties}, for other insertion functions that inherit
text properties from the nearby text in addition to inserting it.
Whitespace inserted by indentation functions also inherits text
properties.

@node Commands for Insertion
@section User-Level Insertion Commands

  This section describes higher-level commands for inserting text,
commands intended primarily for the user but useful also in Lisp
programs.

@deffn Command insert-buffer from-buffer-or-name
This command inserts the entire accessible contents of
@var{from-buffer-or-name} (which must exist) into the current buffer
after point.  It leaves the mark after the inserted text.  The value
is @code{nil}.
@end deffn

@deffn Command self-insert-command count &optional char
@cindex character insertion
@cindex self-insertion
This command inserts the character @var{char} (the last character typed);
it does so @var{count} times, before point, and returns @code{nil}.
Most printing characters are bound to this command.  In routine use,
@code{self-insert-command} is the most frequently called function in Emacs,
but programs rarely use it except to install it on a keymap.

In an interactive call, @var{count} is the numeric prefix argument.

@c FIXME: This variable is obsolete since 23.1.
Self-insertion translates the input character through
@code{translation-table-for-input}.  @xref{Translation of Characters}.

This command calls @code{auto-fill-function} whenever that is
non-@code{nil} and the character inserted is in the table
@code{auto-fill-chars} (@pxref{Auto Filling}).

@c Cross refs reworded to prevent overfull hbox.  --rjc 15mar92
This command performs abbrev expansion if Abbrev mode is enabled and
the inserted character does not have word-constituent
syntax.  (@xref{Abbrevs}, and @ref{Syntax Class Table}.)  It is also
responsible for calling @code{blink-paren-function} when the inserted
character has close parenthesis syntax (@pxref{Blinking}).

@vindex post-self-insert-hook
@vindex self-insert-uses-region-functions
The final thing this command does is to run the hook
@code{post-self-insert-hook}.  You could use this to automatically
reindent text as it is typed, for example.  If any function on this
hook needs to act on the region (@pxref{The Region}), it should make
sure Delete Selection mode (@pxref{Using Region, Delete Selection, ,
emacs, The GNU Emacs Manual}) doesn't delete the region before
@code{post-self-insert-hook} functions are invoked.  The way to do so
is to add a function that returns @code{nil} to
@code{self-insert-uses-region-functions}, a special hook that tells
Delete Selection mode it should not delete the region.

Do not try substituting your own definition of
@code{self-insert-command} for the standard one.  The editor command
loop handles this function specially.
@end deffn

@deffn Command newline &optional number-of-newlines
This command inserts newlines into the current buffer before point.
If @var{number-of-newlines} is supplied, that many newline characters
are inserted.

@cindex newline and Auto Fill mode
This function calls @code{auto-fill-function} if the current column
number is greater than the value of @code{fill-column} and
@var{number-of-newlines} is @code{nil}.  Typically what
@code{auto-fill-function} does is insert a newline; thus, the overall
result in this case is to insert two newlines at different places: one
at point, and another earlier in the line.  @code{newline} does not
auto-fill if @var{number-of-newlines} is non-@code{nil}.

This command indents to the left margin if that is not zero.
@xref{Margins}.

The value returned is @code{nil}.  In an interactive call, @var{count}
is the numeric prefix argument.
@end deffn

@defvar overwrite-mode
This variable controls whether overwrite mode is in effect.  The value
should be @code{overwrite-mode-textual}, @code{overwrite-mode-binary},
or @code{nil}.  @code{overwrite-mode-textual} specifies textual
overwrite mode (treats newlines and tabs specially), and
@code{overwrite-mode-binary} specifies binary overwrite mode (treats
newlines and tabs like any other characters).
@end defvar

@node Deletion
@section Deleting Text
@cindex text deletion

@cindex deleting text vs killing
  Deletion means removing part of the text in a buffer, without saving
it in the kill ring (@pxref{The Kill Ring}).  Deleted text can't be
yanked, but can be reinserted using the undo mechanism (@pxref{Undo}).
Some deletion functions do save text in the kill ring in some special
cases.

  All of the deletion functions operate on the current buffer.

@deffn Command erase-buffer
This function deletes the entire text of the current buffer
(@emph{not} just the accessible portion), leaving it
empty.  If the buffer is read-only, it signals a @code{buffer-read-only}
error; if some of the text in it is read-only, it signals a
@code{text-read-only} error.  Otherwise, it deletes the text without
asking for any confirmation.  It returns @code{nil}.

Normally, deleting a large amount of text from a buffer inhibits further
auto-saving of that buffer because it has shrunk.  However,
@code{erase-buffer} does not do this, the idea being that the future
text is not really related to the former text, and its size should not
be compared with that of the former text.
@end deffn

@deffn Command delete-region start end
This command deletes the text between positions @var{start} and
@var{end} in the current buffer, and returns @code{nil}.  If point was
inside the deleted region, its value afterward is @var{start}.
Otherwise, point relocates with the surrounding text, as markers do.
@end deffn

@defun delete-and-extract-region start end
This function deletes the text between positions @var{start} and
@var{end} in the current buffer, and returns a string containing the
text just deleted.

If point was inside the deleted region, its value afterward is
@var{start}.  Otherwise, point relocates with the surrounding text, as
markers do.
@end defun

@deffn Command delete-char count &optional killp
This command deletes @var{count} characters directly after point, or
before point if @var{count} is negative.  If @var{killp} is
non-@code{nil}, then it saves the deleted characters in the kill ring.

In an interactive call, @var{count} is the numeric prefix argument, and
@var{killp} is the unprocessed prefix argument.  Therefore, if a prefix
argument is supplied, the text is saved in the kill ring.  If no prefix
argument is supplied, then one character is deleted, but not saved in
the kill ring.

The value returned is always @code{nil}.
@end deffn

@deffn Command delete-backward-char count &optional killp
@cindex deleting previous char
This command deletes @var{count} characters directly before point, or
after point if @var{count} is negative.  If @var{killp} is
non-@code{nil}, then it saves the deleted characters in the kill ring.

In an interactive call, @var{count} is the numeric prefix argument, and
@var{killp} is the unprocessed prefix argument.  Therefore, if a prefix
argument is supplied, the text is saved in the kill ring.  If no prefix
argument is supplied, then one character is deleted, but not saved in
the kill ring.

The value returned is always @code{nil}.
@end deffn

@deffn Command backward-delete-char-untabify count &optional killp
@cindex tab deletion
This command deletes @var{count} characters backward, changing tabs
into spaces.  When the next character to be deleted is a tab, it is
first replaced with the proper number of spaces to preserve alignment
and then one of those spaces is deleted instead of the tab.  If
@var{killp} is non-@code{nil}, then the command saves the deleted
characters in the kill ring.

Conversion of tabs to spaces happens only if @var{count} is positive.
If it is negative, exactly @minus{}@var{count} characters after point
are deleted.

In an interactive call, @var{count} is the numeric prefix argument, and
@var{killp} is the unprocessed prefix argument.  Therefore, if a prefix
argument is supplied, the text is saved in the kill ring.  If no prefix
argument is supplied, then one character is deleted, but not saved in
the kill ring.

The value returned is always @code{nil}.
@end deffn

@defopt backward-delete-char-untabify-method
This option specifies how @code{backward-delete-char-untabify} should
deal with whitespace.  Possible values include @code{untabify}, the
default, meaning convert a tab to many spaces and delete one;
@code{hungry}, meaning delete all tabs and spaces before point with
one command; @code{all} meaning delete all tabs, spaces and newlines
before point, and @code{nil}, meaning do nothing special for
whitespace characters.
@end defopt

@node User-Level Deletion
@section User-Level Deletion Commands

  This section describes higher-level commands for deleting text,
commands intended primarily for the user but useful also in Lisp
programs.

@deffn Command delete-horizontal-space &optional backward-only
@cindex deleting whitespace
This function deletes all spaces and tabs around point.  It returns
@code{nil}.

If @var{backward-only} is non-@code{nil}, the function deletes
spaces and tabs before point, but not after point.

In the following examples, we call @code{delete-horizontal-space} four
times, once on each line, with point between the second and third
characters on the line each time.

@example
@group
---------- Buffer: foo ----------
I @point{}thought
I @point{}     thought
We@point{} thought
Yo@point{}u thought
---------- Buffer: foo ----------
@end group

@group
(delete-horizontal-space)   ; @r{Four times.}
     @result{} nil

---------- Buffer: foo ----------
Ithought
Ithought
Wethought
You thought
---------- Buffer: foo ----------
@end group
@end example
@end deffn

@deffn Command delete-indentation &optional join-following-p beg end
This function joins the line point is on to the previous line, deleting
any whitespace at the join and in some cases replacing it with one
space.  If @var{join-following-p} is non-@code{nil},
@code{delete-indentation} joins this line to the following line
instead.  Otherwise, if @var{beg} and @var{end} are non-@code{nil},
this function joins all lines in the region they define.

In an interactive call, @var{join-following-p} is the prefix argument,
and @var{beg} and @var{end} are, respectively, the start and end of
the region if it is active, else @code{nil}.  The function returns
@code{nil}.

If there is a fill prefix, and the second of the lines being joined
starts with the prefix, then @code{delete-indentation} deletes the
fill prefix before joining the lines.  @xref{Margins}.

In the example below, point is located on the line starting
@samp{events}, and it makes no difference if there are trailing spaces
in the preceding line.

@smallexample
@group
---------- Buffer: foo ----------
When in the course of human
@point{}    events, it becomes necessary
---------- Buffer: foo ----------
@end group

(delete-indentation)
     @result{} nil

@group
---------- Buffer: foo ----------
When in the course of human@point{} events, it becomes necessary
---------- Buffer: foo ----------
@end group
@end smallexample

After the lines are joined, the function @code{fixup-whitespace} is
responsible for deciding whether to leave a space at the junction.
@end deffn

@deffn Command fixup-whitespace
This function replaces all the horizontal whitespace surrounding point
with either one space or no space, according to the context.  It
returns @code{nil}.

At the beginning or end of a line, the appropriate amount of space is
none.  Before a character with close parenthesis syntax, or after a
character with open parenthesis or expression-prefix syntax, no space is
also appropriate.  Otherwise, one space is appropriate.  @xref{Syntax
Class Table}.

In the example below, @code{fixup-whitespace} is called the first time
with point before the word @samp{spaces} in the first line.  For the
second invocation, point is directly after the @samp{(}.

@smallexample
@group
---------- Buffer: foo ----------
This has too many     @point{}spaces
This has too many spaces at the start of (@point{}   this list)
---------- Buffer: foo ----------
@end group

@group
(fixup-whitespace)
     @result{} nil
(fixup-whitespace)
     @result{} nil
@end group

@group
---------- Buffer: foo ----------
This has too many spaces
This has too many spaces at the start of (this list)
---------- Buffer: foo ----------
@end group
@end smallexample
@end deffn

@deffn Command just-one-space &optional n
@comment !!SourceFile simple.el
This command replaces any spaces and tabs around point with a single
space, or @var{n} spaces if @var{n} is specified.  It returns
@code{nil}.
@end deffn

@c There is also cycle-spacing, but I cannot see it being useful in
@c Lisp programs, so it is not mentioned here.

@deffn Command delete-blank-lines
This function deletes blank lines surrounding point.  If point is on a
blank line with one or more blank lines before or after it, then all but
one of them are deleted.  If point is on an isolated blank line, then it
is deleted.  If point is on a nonblank line, the command deletes all
blank lines immediately following it.

A blank line is defined as a line containing only tabs and spaces.
@c and the Newline character?

@code{delete-blank-lines} returns @code{nil}.
@end deffn

@deffn Command delete-trailing-whitespace &optional start end
Delete trailing whitespace in the region defined by @var{start} and
@var{end}.

This command deletes whitespace characters after the last
non-whitespace character in each line in the region.

If this command acts on the entire buffer (i.e., if called
interactively with the mark inactive, or called from Lisp with
@var{end} @code{nil}), it also deletes all trailing lines at the end of the
buffer if the variable @code{delete-trailing-lines} is non-@code{nil}.
@end deffn

@node The Kill Ring
@section The Kill Ring
@cindex kill ring

  @dfn{Kill functions} delete text like the deletion functions, but save
it so that the user can reinsert it by @dfn{yanking}.  Most of these
functions have @samp{kill-} in their name.  By contrast, the functions
whose names start with @samp{delete-} normally do not save text for
yanking (though they can still be undone); these are deletion
functions.

  Most of the kill commands are primarily for interactive use, and are
not described here.  What we do describe are the functions provided for
use in writing such commands.  You can use these functions to write
commands for killing text.  When you need to delete text for internal
purposes within a Lisp function, you should normally use deletion
functions, so as not to disturb the kill ring contents.
@xref{Deletion}.

  Killed text is saved for later yanking in the @dfn{kill ring}.  This
is a list that holds a number of recent kills, not just the last text
kill.  We call this a ``ring'' because yanking treats it as having
elements in a cyclic order.  The list is kept in the variable
@code{kill-ring}, and can be operated on with the usual functions for
lists; there are also specialized functions, described in this section,
that treat it as a ring.

  Some people think this use of the word ``kill'' is unfortunate, since
it refers to operations that specifically @emph{do not} destroy the
entities killed.  This is in sharp contrast to ordinary life, in
which death is permanent and killed entities do not come back to
life.  Therefore, other metaphors have been proposed.  For example, the
term ``cut ring'' makes sense to people who, in pre-computer days, used
scissors and paste to cut up and rearrange manuscripts.  However, it
would be difficult to change the terminology now.

@menu
* Kill Ring Concepts::     What text looks like in the kill ring.
* Kill Functions::         Functions that kill text.
* Yanking::                How yanking is done.
* Yank Commands::          Commands that access the kill ring.
* Low-Level Kill Ring::    Functions and variables for kill ring access.
* Internals of Kill Ring:: Variables that hold kill ring data.
@end menu

@node Kill Ring Concepts
@subsection Kill Ring Concepts

  The kill ring records killed text as strings in a list, most recent
first.  A short kill ring, for example, might look like this:

@example
("some text" "a different piece of text" "even older text")
@end example

@noindent
When the list reaches @code{kill-ring-max} entries in length, adding a
new entry automatically deletes the last entry.

  When kill commands are interwoven with other commands, each kill
command makes a new entry in the kill ring.  Multiple kill commands in
succession build up a single kill ring entry, which would be yanked as a
unit; the second and subsequent consecutive kill commands add text to
the entry made by the first one.

  For yanking, one entry in the kill ring is designated the front of
the ring.  Some yank commands rotate the ring by designating a
different element as the front.  But this virtual rotation doesn't
change the list itself---the most recent entry always comes first in the
list.

@node Kill Functions
@subsection Functions for Killing

  @code{kill-region} is the usual subroutine for killing text.  Any
command that calls this function is a kill command (and should
probably have @samp{kill} in its name).  @code{kill-region} puts the
newly killed text in a new element at the beginning of the kill ring or
adds it to the most recent element.  It determines automatically (using
@code{last-command}) whether the previous command was a kill command,
and if so appends the killed text to the most recent entry.

@cindex filtering killed text
  The commands described below can filter the killed text before they
save it in the kill ring.  They call @code{filter-buffer-substring}
(@pxref{Buffer Contents}) to perform the filtering.  By default,
there's no filtering, but major and minor modes and hook functions can
set up filtering, so that text saved in the kill ring is different
from what was in the buffer.

@deffn Command kill-region start end &optional region
This function kills the stretch of text between @var{start} and
@var{end}; but if the optional argument @var{region} is
non-@code{nil}, it ignores @var{start} and @var{end}, and kills the
text in the current region instead.  The text is deleted but saved in
the kill ring, along with its text properties.  The value is always
@code{nil}.

In an interactive call, @var{start} and @var{end} are point and
the mark, and @var{region} is always non-@code{nil}, so the command
always kills the text in the current region.

If the buffer or text is read-only, @code{kill-region} modifies the kill
ring just the same, then signals an error without modifying the buffer.
This is convenient because it lets the user use a series of kill
commands to copy text from a read-only buffer into the kill ring.
@end deffn

@defopt kill-read-only-ok
If this option is non-@code{nil}, @code{kill-region} does not signal an
error if the buffer or text is read-only.  Instead, it simply returns,
updating the kill ring but not changing the buffer.
@end defopt

@deffn Command copy-region-as-kill start end &optional region
This function saves the stretch of text between @var{start} and
@var{end} on the kill ring (including text properties), but does not
delete the text from the buffer.  However, if the optional argument
@var{region} is non-@code{nil}, the function ignores @var{start} and
@var{end}, and saves the current region instead.  It always returns
@code{nil}.

In an interactive call, @var{start} and @var{end} are point and
the mark, and @var{region} is always non-@code{nil}, so the command
always saves the text in the current region.

The command does not set @code{this-command} to @code{kill-region}, so a
subsequent kill command does not append to the same kill ring entry.
@end deffn

@node Yanking
@subsection Yanking

  Yanking means inserting text from the kill ring, but it does not
insert the text blindly.  The @code{yank} command, and related
commands, use @code{insert-for-yank} to perform special processing on
the text before it is inserted.

@defun insert-for-yank string
This function works like @code{insert}, except that it processes the
text in @var{string} according to the @code{yank-handler} text
property, as well as the variables @code{yank-handled-properties} and
@code{yank-excluded-properties} (see below), before inserting the
result into the current buffer.
@end defun

@defun insert-buffer-substring-as-yank buf &optional start end
This function resembles @code{insert-buffer-substring}, except that it
processes the text according to @code{yank-handled-properties} and
@code{yank-excluded-properties}.  (It does not handle the
@code{yank-handler} property, which does not normally occur in buffer
text anyway.)
@end defun

@c FIXME: Add an index for yank-handler.
  If you put a @code{yank-handler} text property on all or part of a
string, that alters how @code{insert-for-yank} inserts the string.  If
different parts of the string have different @code{yank-handler}
values (comparison being done with @code{eq}), each substring is
handled separately.  The property value must be a list of one to four
elements, with the following format (where elements after the first
may be omitted):

@example
(@var{function} @var{param} @var{noexclude} @var{undo})
@end example

  Here is what the elements do:

@table @var
@item function
When @var{function} is non-@code{nil}, it is called instead of
@code{insert} to insert the string, with one argument---the string to
insert.

@item param
If @var{param} is present and non-@code{nil}, it replaces @var{string}
(or the substring of @var{string} being processed) as the object
passed to @var{function} (or @code{insert}).  For example, if
@var{function} is @code{yank-rectangle}, @var{param} should be a list
of strings to insert as a rectangle.

@item noexclude
If @var{noexclude} is present and non-@code{nil}, that disables the
normal action of @code{yank-handled-properties} and
@code{yank-excluded-properties} on the inserted string.

@item undo
If @var{undo} is present and non-@code{nil}, it is a function that will be
called by @code{yank-pop} to undo the insertion of the current object.
It is called with two arguments, the start and end of the current
region.  @var{function} can set @code{yank-undo-function} to override
the @var{undo} value.
@end table

@cindex yanking and text properties
@defopt yank-handled-properties
This variable specifies special text property handling conditions for
yanked text.  It takes effect after the text has been inserted (either
normally, or via the @code{yank-handler} property), and prior to
@code{yank-excluded-properties} taking effect.

The value should be an alist of elements @code{(@var{prop}
. @var{fun})}.  Each alist element is handled in order.  The inserted
text is scanned for stretches of text having text properties @code{eq}
to @var{prop}; for each such stretch, @var{fun} is called with three
arguments: the value of the property, and the start and end positions
of the text.
@end defopt

@defopt yank-excluded-properties
The value of this variable is the list of properties to remove from
inserted text.  Its default value contains properties that might lead
to annoying results, such as causing the text to respond to the mouse
or specifying key bindings.  It takes effect after
@code{yank-handled-properties}.
@end defopt


@node Yank Commands
@subsection Functions for Yanking

  This section describes higher-level commands for yanking, which are
intended primarily for the user but useful also in Lisp programs.
Both @code{yank} and @code{yank-pop} honor the
@code{yank-excluded-properties} variable and @code{yank-handler} text
property (@pxref{Yanking}).

@deffn Command yank &optional arg
@cindex inserting killed text
This command inserts before point the text at the front of the kill
ring.  It sets the mark at the beginning of that text, using
@code{push-mark} (@pxref{The Mark}), and puts point at the end.

If @var{arg} is a non-@code{nil} list (which occurs interactively when
the user types @kbd{C-u} with no digits), then @code{yank} inserts the
text as described above, but puts point before the yanked text and
sets the mark after it.

If @var{arg} is a number, then @code{yank} inserts the @var{arg}th
most recently killed text---the @var{arg}th element of the kill ring
list, counted cyclically from the front, which is considered the
first element for this purpose.

@code{yank} does not alter the contents of the kill ring, unless it
used text provided by another program, in which case it pushes that text
onto the kill ring.  However if @var{arg} is an integer different from
one, it rotates the kill ring to place the yanked string at the front.

@code{yank} returns @code{nil}.
@end deffn

@deffn Command yank-pop &optional arg
This command replaces the just-yanked entry from the kill ring with a
different entry from the kill ring.

This is allowed only immediately after a @code{yank} or another
@code{yank-pop}.  At such a time, the region contains text that was just
inserted by yanking.  @code{yank-pop} deletes that text and inserts in
its place a different piece of killed text.  It does not add the deleted
text to the kill ring, since it is already in the kill ring somewhere.
It does however rotate the kill ring to place the newly yanked string at
the front.

If @var{arg} is @code{nil}, then the replacement text is the previous
element of the kill ring.  If @var{arg} is numeric, the replacement is
the @var{arg}th previous kill.  If @var{arg} is negative, a more recent
kill is the replacement.

The sequence of kills in the kill ring wraps around, so that after the
oldest one comes the newest one, and before the newest one goes the
oldest.

The return value is always @code{nil}.
@end deffn

@defvar yank-undo-function
If this variable is non-@code{nil}, the function @code{yank-pop} uses
its value instead of @code{delete-region} to delete the text
inserted by the previous @code{yank} or
@code{yank-pop} command.  The value must be a function of two
arguments, the start and end of the current region.

The function @code{insert-for-yank} automatically sets this variable
according to the @var{undo} element of the @code{yank-handler}
text property, if there is one.
@end defvar

@node Low-Level Kill Ring
@subsection Low-Level Kill Ring

  These functions and variables provide access to the kill ring at a
lower level, but are still convenient for use in Lisp programs,
because they take care of interaction with window system selections
(@pxref{Window System Selections}).

@defun current-kill n &optional do-not-move
The function @code{current-kill} rotates the yanking pointer, which
designates the front of the kill ring, by @var{n} places (from newer
kills to older ones), and returns the text at that place in the ring.

If the optional second argument @var{do-not-move} is non-@code{nil},
then @code{current-kill} doesn't alter the yanking pointer; it just
returns the @var{n}th kill, counting from the current yanking pointer.

If @var{n} is zero, indicating a request for the latest kill,
@code{current-kill} calls the value of
@code{interprogram-paste-function} (documented below) before
consulting the kill ring.  If that value is a function and calling it
returns a string or a list of several strings, @code{current-kill}
pushes the strings onto the kill ring and returns the first string.
It also sets the yanking pointer to point to the kill-ring entry of
the first string returned by @code{interprogram-paste-function},
regardless of the value of @var{do-not-move}.  Otherwise,
@code{current-kill} does not treat a zero value for @var{n} specially:
it returns the entry pointed at by the yanking pointer and does not
move the yanking pointer.
@end defun

@defun kill-new string &optional replace
This function pushes the text @var{string} onto the kill ring and
makes the yanking pointer point to it.  It discards the oldest entry
if appropriate.  It also invokes the values of
@code{interprogram-paste-function} (subject to
the user option @code{save-interprogram-paste-before-kill})
and @code{interprogram-cut-function} (see below).

If @var{replace} is non-@code{nil}, then @code{kill-new} replaces the
first element of the kill ring with @var{string}, rather than pushing
@var{string} onto the kill ring.
@end defun

@defun kill-append string before-p
This function appends the text @var{string} to the first entry in the
kill ring and makes the yanking pointer point to the combined entry.
Normally @var{string} goes at the end of the entry, but if
@var{before-p} is non-@code{nil}, it goes at the beginning.  This
function calls @code{kill-new} as a subroutine, thus causing the
values of @code{interprogram-cut-function} and possibly
@code{interprogram-paste-function} (see below) to be invoked by
extension.
@end defun

@defvar interprogram-paste-function
This variable provides a way of transferring killed text from other
programs, when you are using a window system.  Its value should be
@code{nil} or a function of no arguments.

If the value is a function, @code{current-kill} calls it to get the
most recent kill.  If the function returns a non-@code{nil} value,
then that value is used as the most recent kill.  If it returns
@code{nil}, then the front of the kill ring is used.

To facilitate support for window systems that support multiple
selections, this function may also return a list of strings.  In that
case, the first string is used as the most recent kill, and all
the other strings are pushed onto the kill ring, for easy access by
@code{yank-pop}.

The normal use of this function is to get the window system's
clipboard as the most recent kill, even if the selection belongs to
another application.  @xref{Window System Selections}.  However, if
the clipboard contents come from the current Emacs session, this
function should return @code{nil}.
@end defvar

@defvar interprogram-cut-function
This variable provides a way of communicating killed text to other
programs, when you are using a window system.  Its value should be
@code{nil} or a function of one required argument.

If the value is a function, @code{kill-new} and @code{kill-append} call
it with the new first element of the kill ring as the argument.

The normal use of this function is to put newly killed text in the
window system's clipboard.  @xref{Window System Selections}.
@end defvar

@node Internals of Kill Ring
@subsection Internals of the Kill Ring

  The variable @code{kill-ring} holds the kill ring contents, in the
form of a list of strings.  The most recent kill is always at the front
of the list.

  The @code{kill-ring-yank-pointer} variable points to a link in the
kill ring list, whose @sc{car} is the text to yank next.  We say it
identifies the front of the ring.  Moving
@code{kill-ring-yank-pointer} to a different link is called
@dfn{rotating the kill ring}.  We call the kill ring a ``ring'' because
the functions that move the yank pointer wrap around from the end of the
list to the beginning, or vice-versa.  Rotation of the kill ring is
virtual; it does not change the value of @code{kill-ring}.

  Both @code{kill-ring} and @code{kill-ring-yank-pointer} are Lisp
variables whose values are normally lists.  The word ``pointer'' in the
name of the @code{kill-ring-yank-pointer} indicates that the variable's
purpose is to identify one element of the list for use by the next yank
command.

  The value of @code{kill-ring-yank-pointer} is always @code{eq} to one
of the links in the kill ring list.  The element it identifies is the
@sc{car} of that link.  Kill commands, which change the kill ring, also
set this variable to the value of @code{kill-ring}.  The effect is to
rotate the ring so that the newly killed text is at the front.

  Here is a diagram that shows the variable @code{kill-ring-yank-pointer}
pointing to the second entry in the kill ring @code{("some text" "a
different piece of text" "yet older text")}.

@example
@group
kill-ring                  ---- kill-ring-yank-pointer
  |                       |
  |                       v
  |     --- ---          --- ---      --- ---
   --> |   |   |------> |   |   |--> |   |   |--> nil
        --- ---          --- ---      --- ---
         |                |            |
         |                |            |
         |                |             -->"yet older text"
         |                |
         |                 --> "a different piece of text"
         |
          --> "some text"
@end group
@end example

@noindent
This state of affairs might occur after @kbd{C-y} (@code{yank})
immediately followed by @kbd{M-y} (@code{yank-pop}).

@defvar kill-ring
This variable holds the list of killed text sequences, most recently
killed first.
@end defvar

@defvar kill-ring-yank-pointer
This variable's value indicates which element of the kill ring is at the
front of the ring for yanking.  More precisely, the value is a tail
of the value of @code{kill-ring}, and its @sc{car} is the kill string
that @kbd{C-y} should yank.
@end defvar

@defopt kill-ring-max
The value of this variable is the maximum length to which the kill
ring can grow, before elements are thrown away at the end.  The default
value for @code{kill-ring-max} is 60.
@end defopt

@node Undo
@section Undo
@cindex redo

  Most buffers have an @dfn{undo list}, which records all changes made
to the buffer's text so that they can be undone.  (The buffers that
don't have one are usually special-purpose buffers for which Emacs
assumes that undoing is not useful.  In particular, any buffer whose
name begins with a space has its undo recording off by default;
see @ref{Buffer Names}.)  All the primitives that modify the
text in the buffer automatically add elements to the front of the undo
list, which is in the variable @code{buffer-undo-list}.

@defvar buffer-undo-list
This buffer-local variable's value is the undo list of the current
buffer.  A value of @code{t} disables the recording of undo information.
@end defvar

Here are the kinds of elements an undo list can have:

@table @code
@item @var{position}
This kind of element records a previous value of point; undoing this
element moves point to @var{position}.  Ordinary cursor motion does not
make any sort of undo record, but deletion operations use these entries
to record where point was before the command.

@item (@var{beg} . @var{end})
This kind of element indicates how to delete text that was inserted.
Upon insertion, the text occupied the range @var{beg}--@var{end} in the
buffer.

@item (@var{text} . @var{position})
This kind of element indicates how to reinsert text that was deleted.
The deleted text itself is the string @var{text}.  The place to
reinsert it is @code{(abs @var{position})}.  If @var{position} is
positive, point was at the beginning of the deleted text, otherwise it
was at the end.  Zero or more (@var{marker} . @var{adjustment})
elements follow immediately after this element.

@item (t . @var{time-flag})
This kind of element indicates that an unmodified buffer became
modified.  A @var{time-flag} that is a non-integer Lisp timestamp
represents the visited file's modification time as of
when it was previously visited or saved, using the same format as
@code{current-time}; see @ref{Time of Day}.
A @var{time-flag} of 0 means the buffer does not correspond to any file;
@minus{}1 means the visited file previously did not exist.
@code{primitive-undo} uses these
values to determine whether to mark the buffer as unmodified once again;
it does so only if the file's status matches that of @var{time-flag}.

@item (nil @var{property} @var{value} @var{beg} . @var{end})
This kind of element records a change in a text property.
Here's how you might undo the change:

@example
(put-text-property @var{beg} @var{end} @var{property} @var{value})
@end example

@item (@var{marker} . @var{adjustment})
This kind of element records the fact that the marker @var{marker} was
relocated due to deletion of surrounding text, and that it moved
@var{adjustment} character positions.  If the marker's location is
consistent with the (@var{text} . @var{position}) element preceding it
in the undo list, then undoing this element moves @var{marker}
@minus{} @var{adjustment} characters.

@item (apply @var{funname} . @var{args})
This is an extensible undo item, which is undone by calling
@var{funname} with arguments @var{args}.

@item (apply @var{delta} @var{beg} @var{end} @var{funname} . @var{args})
This is an extensible undo item, which records a change limited to the
range @var{beg} to @var{end}, which increased the size of the buffer
by @var{delta} characters.  It is undone by calling @var{funname} with
arguments @var{args}.

This kind of element enables undo limited to a region to determine
whether the element pertains to that region.

@item nil
This element is a boundary.  The elements between two boundaries are
called a @dfn{change group}; normally, each change group corresponds to
one keyboard command, and undo commands normally undo an entire group as
a unit.
@end table

@defun undo-boundary
This function places a boundary element in the undo list.  The undo
command stops at such a boundary, and successive undo commands undo
to earlier and earlier boundaries.  This function returns @code{nil}.

Calling this function explicitly is useful for splitting the effects of
a command into more than one unit.  For example, @code{query-replace}
calls @code{undo-boundary} after each replacement, so that the user can
undo individual replacements one by one.

Mostly, however, this function is called automatically at an
appropriate time.
@end defun

@defun undo-auto-amalgamate
@cindex amalgamating commands, and undo
The editor command loop automatically calls @code{undo-boundary} just
before executing each key sequence, so that each undo normally undoes
the effects of one command.  A few exceptional commands are
@dfn{amalgamating}: these commands generally cause small changes to
buffers, so with these a boundary is inserted only every 20th command,
allowing the changes to be undone as a group.  By default, the commands
@code{self-insert-command}, which produces self-inserting input
characters (@pxref{Commands for Insertion}), and @code{delete-char},
which deletes characters (@pxref{Deletion}), are amalgamating.
Where a command affects the contents of several buffers, as may happen,
for example, when a function on the @code{post-command-hook} affects a
buffer other than the @code{current-buffer}, then @code{undo-boundary}
will be called in each of the affected buffers.
@end defun

@defvar undo-auto-current-boundary-timer
Some buffers, such as process buffers, can change even when no
commands are executing.  In these cases, @code{undo-boundary} is
normally called periodically by the timer in this variable.  Setting
this variable to non-@code{nil} prevents this behavior.
@end defvar

@defvar undo-in-progress
This variable is normally @code{nil}, but the undo commands bind it to
@code{t}.  This is so that various kinds of change hooks can tell when
they're being called for the sake of undoing.
@end defvar

@defun primitive-undo count list
This is the basic function for undoing elements of an undo list.
It undoes the first @var{count} elements of @var{list}, returning
the rest of @var{list}.

@code{primitive-undo} adds elements to the buffer's undo list when it
changes the buffer.  Undo commands avoid confusion by saving the undo
list value at the beginning of a sequence of undo operations.  Then the
undo operations use and update the saved value.  The new elements added
by undoing are not part of this saved value, so they don't interfere with
continuing to undo.

This function does not bind @code{undo-in-progress}.
@end defun

@node Maintaining Undo
@section Maintaining Undo Lists

  This section describes how to enable and disable undo information for
a given buffer.  It also explains how the undo list is truncated
automatically so it doesn't get too big.

  Recording of undo information in a newly created buffer is normally
enabled to start with; but if the buffer name starts with a space, the
undo recording is initially disabled.  You can explicitly enable or
disable undo recording with the following two functions, or by setting
@code{buffer-undo-list} yourself.

@deffn Command buffer-enable-undo &optional buffer-or-name
This command enables recording undo information for buffer
@var{buffer-or-name}, so that subsequent changes can be undone.  If no
argument is supplied, then the current buffer is used.  This function
does nothing if undo recording is already enabled in the buffer.  It
returns @code{nil}.

In an interactive call, @var{buffer-or-name} is the current buffer.
You cannot specify any other buffer.
@end deffn

@deffn Command buffer-disable-undo &optional buffer-or-name
@cindex disabling undo
This function discards the undo list of @var{buffer-or-name}, and disables
further recording of undo information.  As a result, it is no longer
possible to undo either previous changes or any subsequent changes.  If
the undo list of @var{buffer-or-name} is already disabled, this function
has no effect.

In an interactive call, BUFFER-OR-NAME is the current buffer.  You
cannot specify any other buffer.  This function returns @code{nil}.
@end deffn

  As editing continues, undo lists get longer and longer.  To prevent
them from using up all available memory space, garbage collection trims
them back to size limits you can set.  (For this purpose, the size
of an undo list measures the cons cells that make up the list, plus the
strings of deleted text.)  Three variables control the range of acceptable
sizes: @code{undo-limit}, @code{undo-strong-limit} and
@code{undo-outer-limit}.  In these variables, size is counted as the
number of bytes occupied, which includes both saved text and other
data.

@defopt undo-limit
This is the soft limit for the acceptable size of an undo list.  The
change group at which this size is exceeded is the last one kept.
@end defopt

@defopt undo-strong-limit
This is the upper limit for the acceptable size of an undo list.  The
change group at which this size is exceeded is discarded itself (along
with all older change groups).  There is one exception: the very latest
change group is only discarded if it exceeds @code{undo-outer-limit}.
@end defopt

@defopt undo-outer-limit
If at garbage collection time the undo info for the current command
exceeds this limit, Emacs discards the info and displays a warning.
This is a last ditch limit to prevent memory overflow.
@end defopt

@defopt undo-ask-before-discard
If this variable is non-@code{nil}, when the undo info exceeds
@code{undo-outer-limit}, Emacs asks in the echo area whether to
discard the info.  The default value is @code{nil}, which means to
discard it automatically.

This option is mainly intended for debugging.  Garbage collection is
inhibited while the question is asked, which means that Emacs might
leak memory if the user waits too long before answering the question.
@end defopt

@node Filling
@section Filling
@cindex filling text

  @dfn{Filling} means adjusting the lengths of lines (by moving the line
breaks) so that they are nearly (but no greater than) a specified
maximum width.  Additionally, lines can be @dfn{justified}, which means
inserting spaces to make the left and/or right margins line up
precisely.  The width is controlled by the variable @code{fill-column}.
For ease of reading, lines should be no longer than 70 or so columns.

  You can use Auto Fill mode (@pxref{Auto Filling}) to fill text
automatically as you insert it, but changes to existing text may leave
it improperly filled.  Then you must fill the text explicitly.

  Most of the commands in this section return values that are not
meaningful.  All the functions that do filling take note of the current
left margin, current right margin, and current justification style
(@pxref{Margins}).  If the current justification style is
@code{none}, the filling functions don't actually do anything.

  Several of the filling functions have an argument @var{justify}.
If it is non-@code{nil}, that requests some kind of justification.  It
can be @code{left}, @code{right}, @code{full}, or @code{center}, to
request a specific style of justification.  If it is @code{t}, that
means to use the current justification style for this part of the text
(see @code{current-justification}, below).  Any other value is treated
as @code{full}.

  When you call the filling functions interactively, using a prefix
argument implies the value @code{full} for @var{justify}.

@deffn Command fill-paragraph &optional justify region
This command fills the paragraph at or after point.  If
@var{justify} is non-@code{nil}, each line is justified as well.
It uses the ordinary paragraph motion commands to find paragraph
boundaries.  @xref{Paragraphs,,, emacs, The GNU Emacs Manual}.

When @var{region} is non-@code{nil}, then if Transient Mark mode is
enabled and the mark is active, this command calls @code{fill-region}
to fill all the paragraphs in the region, instead of filling only the
current paragraph.  When this command is called interactively,
@var{region} is @code{t}.
@end deffn

@deffn Command fill-region start end &optional justify nosqueeze to-eop
This command fills each of the paragraphs in the region from @var{start}
to @var{end}.  It justifies as well if @var{justify} is
non-@code{nil}.

If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
other than line breaks untouched.  If @var{to-eop} is non-@code{nil},
that means to keep filling to the end of the paragraph---or the next hard
newline, if @code{use-hard-newlines} is enabled (see below).

The variable @code{paragraph-separate} controls how to distinguish
paragraphs.  @xref{Standard Regexps}.
@end deffn

@deffn Command fill-individual-paragraphs start end &optional justify citation-regexp
This command fills each paragraph in the region according to its
individual fill prefix.  Thus, if the lines of a paragraph were indented
with spaces, the filled paragraph will remain indented in the same
fashion.

The first two arguments, @var{start} and @var{end}, are the beginning
and end of the region to be filled.  The third and fourth arguments,
@var{justify} and @var{citation-regexp}, are optional.  If
@var{justify} is non-@code{nil}, the paragraphs are justified as
well as filled.  If @var{citation-regexp} is non-@code{nil}, it means the
function is operating on a mail message and therefore should not fill
the header lines.  If @var{citation-regexp} is a string, it is used as
a regular expression; if it matches the beginning of a line, that line
is treated as a citation marker.

@c FIXME: "That mode" is confusing.  It isn't a major/minor mode.
Ordinarily, @code{fill-individual-paragraphs} regards each change in
indentation as starting a new paragraph.  If
@code{fill-individual-varying-indent} is non-@code{nil}, then only
separator lines separate paragraphs.  That mode can handle indented
paragraphs with additional indentation on the first line.
@end deffn

@defopt fill-individual-varying-indent
This variable alters the action of @code{fill-individual-paragraphs} as
described above.
@end defopt

@deffn Command fill-region-as-paragraph start end &optional justify nosqueeze squeeze-after
This command considers a region of text as a single paragraph and fills
it.  If the region was made up of many paragraphs, the blank lines
between paragraphs are removed.  This function justifies as well as
filling when @var{justify} is non-@code{nil}.

If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
other than line breaks untouched.  If @var{squeeze-after} is
non-@code{nil}, it specifies a position in the region, and means don't
canonicalize spaces before that position.

In Adaptive Fill mode, this command calls @code{fill-context-prefix} to
choose a fill prefix by default.  @xref{Adaptive Fill}.
@end deffn

@deffn Command justify-current-line &optional how eop nosqueeze
This command inserts spaces between the words of the current line so
that the line ends exactly at @code{fill-column}.  It returns
@code{nil}.

The argument @var{how}, if non-@code{nil} specifies explicitly the style
of justification.  It can be @code{left}, @code{right}, @code{full},
@code{center}, or @code{none}.  If it is @code{t}, that means to
follow specified justification style (see @code{current-justification},
below).  @code{nil} means to do full justification.

If @var{eop} is non-@code{nil}, that means do only left-justification
if @code{current-justification} specifies full justification.  This is
used for the last line of a paragraph; even if the paragraph as a
whole is fully justified, the last line should not be.

If @var{nosqueeze} is non-@code{nil}, that means do not change interior
whitespace.
@end deffn

@defopt default-justification
This variable's value specifies the style of justification to use for
text that doesn't specify a style with a text property.  The possible
values are @code{left}, @code{right}, @code{full}, @code{center}, or
@code{none}.  The default value is @code{left}.
@end defopt

@defun current-justification
This function returns the proper justification style to use for filling
the text around point.

This returns the value of the @code{justification} text property at
point, or the variable @code{default-justification} if there is no such
text property.  However, it returns @code{nil} rather than @code{none}
to mean ``don't justify''.
@end defun

@defopt sentence-end-double-space
@anchor{Definition of sentence-end-double-space}
If this variable is non-@code{nil}, a period followed by just one space
does not count as the end of a sentence, and the filling functions
avoid breaking the line at such a place.
@end defopt

@defopt sentence-end-without-period
If this variable is non-@code{nil}, a sentence can end without a
period.  This is used for languages like Thai, where sentences end
with a double space but without a period.
@end defopt

@defopt sentence-end-without-space
If this variable is non-@code{nil}, it should be a string of
characters that can end a sentence without following spaces.
@end defopt

@defopt fill-separate-heterogeneous-words-with-space
If this variable is non-@code{nil}, two words of different kind (e.g.,
English and CJK) will be separated with a space when concatenating one
that is in the end of a line and the other that is in the beginning of
the next line for filling.
@end defopt

@defvar fill-paragraph-function
This variable provides a way to override the filling of paragraphs.
If its value is non-@code{nil}, @code{fill-paragraph} calls this
function to do the work.  If the function returns a non-@code{nil}
value, @code{fill-paragraph} assumes the job is done, and immediately
returns that value.

The usual use of this feature is to fill comments in programming
language modes.  If the function needs to fill a paragraph in the usual
way, it can do so as follows:

@example
(let ((fill-paragraph-function nil))
  (fill-paragraph arg))
@end example
@end defvar

@defvar fill-forward-paragraph-function
This variable provides a way to override how the filling functions,
such as @code{fill-region} and @code{fill-paragraph}, move forward to
the next paragraph.  Its value should be a function, which is called
with a single argument @var{n}, the number of paragraphs to move, and
should return the difference between @var{n} and the number of
paragraphs actually moved.  The default value of this variable is
@code{forward-paragraph}.  @xref{Paragraphs,,, emacs, The GNU Emacs
Manual}.
@end defvar

@defvar use-hard-newlines
If this variable is non-@code{nil}, the filling functions do not delete
newlines that have the @code{hard} text property.  These hard
newlines act as paragraph separators.  @xref{Hard and Soft
Newlines,, Hard and Soft Newlines, emacs, The GNU Emacs Manual}.
@end defvar

@node Margins
@section Margins for Filling
@cindex margins, filling

@defopt fill-prefix
This buffer-local variable, if non-@code{nil}, specifies a string of
text that appears at the beginning of normal text lines and should be
disregarded when filling them.  Any line that fails to start with the
fill prefix is considered the start of a paragraph; so is any line
that starts with the fill prefix followed by additional whitespace.
Lines that start with the fill prefix but no additional whitespace are
ordinary text lines that can be filled together.  The resulting filled
lines also start with the fill prefix.

The fill prefix follows the left margin whitespace, if any.
@end defopt

@defopt fill-column
This buffer-local variable specifies the maximum width of filled lines.
Its value should be an integer, which is a number of columns.  All the
filling, justification, and centering commands are affected by this
variable, including Auto Fill mode (@pxref{Auto Filling}).

As a practical matter, if you are writing text for other people to
read, you should set @code{fill-column} to no more than 70.  Otherwise
the line will be too long for people to read comfortably, and this can
make the text seem clumsy.

The default value for @code{fill-column} is 70.
@end defopt

@deffn Command set-left-margin from to margin
This sets the @code{left-margin} property on the text from @var{from} to
@var{to} to the value @var{margin}.  If Auto Fill mode is enabled, this
command also refills the region to fit the new margin.
@end deffn

@deffn Command set-right-margin from to margin
This sets the @code{right-margin} property on the text from @var{from}
to @var{to} to the value @var{margin}.  If Auto Fill mode is enabled,
this command also refills the region to fit the new margin.
@end deffn

@defun current-left-margin
This function returns the proper left margin value to use for filling
the text around point.  The value is the sum of the @code{left-margin}
property of the character at the start of the current line (or zero if
none), and the value of the variable @code{left-margin}.
@end defun

@defun current-fill-column
This function returns the proper fill column value to use for filling
the text around point.  The value is the value of the @code{fill-column}
variable, minus the value of the @code{right-margin} property of the
character after point.
@end defun

@deffn Command move-to-left-margin &optional n force
This function moves point to the left margin of the current line.  The
column moved to is determined by calling the function
@code{current-left-margin}.  If the argument @var{n} is non-@code{nil},
@code{move-to-left-margin} moves forward @var{n}@minus{}1 lines first.

If @var{force} is non-@code{nil}, that says to fix the line's
indentation if that doesn't match the left margin value.
@end deffn

@defun delete-to-left-margin &optional from to
This function removes left margin indentation from the text between
@var{from} and @var{to}.  The amount of indentation to delete is
determined by calling @code{current-left-margin}.  In no case does this
function delete non-whitespace.  If @var{from} and @var{to} are omitted,
they default to the whole buffer.
@end defun

@defun indent-to-left-margin
This function adjusts the indentation at the beginning of the current
line to the value specified by the variable @code{left-margin}.  (That
may involve either inserting or deleting whitespace.)  This function
is value of @code{indent-line-function} in Paragraph-Indent Text mode.
@end defun

@defopt left-margin
This variable specifies the base left margin column.  In Fundamental
mode, @key{RET} indents to this column.  This variable automatically
becomes buffer-local when set in any fashion.
@end defopt

@defopt fill-nobreak-predicate
This variable gives major modes a way to specify not to break a line
at certain places.  Its value should be a list of functions.  Whenever
filling considers breaking the line at a certain place in the buffer,
it calls each of these functions with no arguments and with point
located at that place.  If any of the functions returns
non-@code{nil}, then the line won't be broken there.
@end defopt

@node Adaptive Fill
@section Adaptive Fill Mode
@c @cindex Adaptive Fill mode  "adaptive-fill-mode" is adjacent.

  When @dfn{Adaptive Fill Mode} is enabled, Emacs determines the fill
prefix automatically from the text in each paragraph being filled
rather than using a predetermined value.  During filling, this fill
prefix gets inserted at the start of the second and subsequent lines
of the paragraph as described in @ref{Filling}, and in @ref{Auto
Filling}.

@defopt adaptive-fill-mode
Adaptive Fill mode is enabled when this variable is non-@code{nil}.
It is @code{t} by default.
@end defopt

@defun fill-context-prefix from to
This function implements the heart of Adaptive Fill mode; it chooses a
fill prefix based on the text between @var{from} and @var{to},
typically the start and end of a paragraph.  It does this by looking
at the first two lines of the paragraph, based on the variables
described below.
@c The optional argument first-line-regexp is not documented
@c because it exists for internal purposes and might be eliminated
@c in the future.

Usually, this function returns the fill prefix, a string.  However,
before doing this, the function makes a final check (not specially
mentioned in the following) that a line starting with this prefix
wouldn't look like the start of a paragraph.  Should this happen, the
function signals the anomaly by returning @code{nil} instead.

In detail, @code{fill-context-prefix} does this:

@enumerate
@item
It takes a candidate for the fill prefix from the first line---it
tries first the function in @code{adaptive-fill-function} (if any),
then the regular expression @code{adaptive-fill-regexp} (see below).
The first non-@code{nil} result of these, or the empty string if
they're both @code{nil}, becomes the first line's candidate.
@item
If the paragraph has as yet only one line, the function tests the
validity of the prefix candidate just found.  The function then
returns the candidate if it's valid, or a string of spaces otherwise.
(see the description of @code{adaptive-fill-first-line-regexp} below).
@item
When the paragraph already has two lines, the function next looks for
a prefix candidate on the second line, in just the same way it did for
the first line.  If it doesn't find one, it returns @code{nil}.
@item
The function now compares the two candidate prefixes heuristically: if
the non-whitespace characters in the line 2 candidate occur in the
same order in the line 1 candidate, the function returns the line 2
candidate.  Otherwise, it returns the largest initial substring which
is common to both candidates (which might be the empty string).
@end enumerate
@end defun

@defopt adaptive-fill-regexp
Adaptive Fill mode matches this regular expression against the text
starting after the left margin whitespace (if any) on a line; the
characters it matches are that line's candidate for the fill prefix.

The default value matches whitespace with certain punctuation
characters intermingled.
@end defopt

@defopt adaptive-fill-first-line-regexp
Used only in one-line paragraphs, this regular expression acts as an
additional check of the validity of the one available candidate fill
prefix: the candidate must match this regular expression, or match
@code{comment-start-skip}.  If it doesn't, @code{fill-context-prefix}
replaces the candidate with a string of spaces of the same width
as it.

The default value of this variable is @w{@code{"\\`[ \t]*\\'"}}, which
matches only a string of whitespace.  The effect of this default is to
force the fill prefixes found in one-line paragraphs always to be pure
whitespace.
@end defopt

@defopt adaptive-fill-function
You can specify more complex ways of choosing a fill prefix
automatically by setting this variable to a function.  The function is
called with point after the left margin (if any) of a line, and it
must preserve point.  It should return either that line's fill
prefix or @code{nil}, meaning it has failed to determine a prefix.
@end defopt

@node Auto Filling
@section Auto Filling
@cindex filling, automatic
@cindex Auto Fill mode

Auto Fill mode is a minor mode that fills lines automatically as text is
inserted.  @xref{Auto Fill,,, emacs, The GNU Emacs Manual}.  This
section describes some variables used by Auto Fill mode.  For a
description of functions that you can call explicitly to fill and
justify existing text, see @ref{Filling}.

  Auto Fill mode also enables the functions that change the margins and
justification style to refill portions of the text.  @xref{Margins}.

@defvar auto-fill-function
The value of this buffer-local variable should be a function (of no
arguments) to be called after self-inserting a character from the table
@code{auto-fill-chars}, see below.  It may be @code{nil}, in which case
nothing special is done in that case.

The value of @code{auto-fill-function} is @code{do-auto-fill} when Auto
Fill mode is enabled.  That is a function whose sole purpose is to
implement the usual strategy for breaking a line.
@end defvar

@defvar normal-auto-fill-function
This variable specifies the function to use for
@code{auto-fill-function}, if and when Auto Fill is turned on.  Major
modes can set buffer-local values for this variable to alter how Auto
Fill works.
@end defvar

@defvar auto-fill-chars
A char table of characters which invoke @code{auto-fill-function} when
self-inserted---space and newline in most language environments.  They
have an entry @code{t} in the table.
@end defvar

@defopt comment-auto-fill-only-comments
This variable, if non-@code{nil}, means to fill lines automatically
within comments only.  More precisely, this means that if a comment
syntax was defined for the current buffer, then self-inserting a
character outside of a comment will not call @code{auto-fill-function}.
@end defopt


@node Sorting
@section Sorting Text
@cindex sorting text

  The sorting functions described in this section all rearrange text in
a buffer.  This is in contrast to the function @code{sort}, which
rearranges the order of the elements of a list (@pxref{Rearrangement}).
The values returned by these functions are not meaningful.

@defun sort-subr reverse nextrecfun endrecfun &optional startkeyfun endkeyfun predicate
This function is the general text-sorting routine that subdivides a
buffer into records and then sorts them.  Most of the commands in this
section use this function.

To understand how @code{sort-subr} works, consider the whole accessible
portion of the buffer as being divided into disjoint pieces called
@dfn{sort records}.  The records may or may not be contiguous, but they
must not overlap.  A portion of each sort record (perhaps all of it) is
designated as the sort key.  Sorting rearranges the records in order by
their sort keys.

Usually, the records are rearranged in order of ascending sort key.
If the first argument to the @code{sort-subr} function, @var{reverse},
is non-@code{nil}, the sort records are rearranged in order of
descending sort key.

The next four arguments to @code{sort-subr} are functions that are
called to move point across a sort record.  They are called many times
from within @code{sort-subr}.

@enumerate
@item
@var{nextrecfun} is called with point at the end of a record.  This
function moves point to the start of the next record.  The first record
is assumed to start at the position of point when @code{sort-subr} is
called.  Therefore, you should usually move point to the beginning of
the buffer before calling @code{sort-subr}.

This function can indicate there are no more sort records by leaving
point at the end of the buffer.

@item
@var{endrecfun} is called with point within a record.  It moves point to
the end of the record.

@item
@var{startkeyfun} is called to move point from the start of a record to
the start of the sort key.  This argument is optional; if it is omitted,
the whole record is the sort key.  If supplied, the function should
either return a non-@code{nil} value to be used as the sort key, or
return @code{nil} to indicate that the sort key is in the buffer
starting at point.  In the latter case, @var{endkeyfun} is called to
find the end of the sort key.

@item
@var{endkeyfun} is called to move point from the start of the sort key
to the end of the sort key.  This argument is optional.  If
@var{startkeyfun} returns @code{nil} and this argument is omitted (or
@code{nil}), then the sort key extends to the end of the record.  There
is no need for @var{endkeyfun} if @var{startkeyfun} returns a
non-@code{nil} value.
@end enumerate

The argument @var{predicate} is the function to use to compare keys.
If keys are numbers, it defaults to @code{<}; otherwise it defaults to
@code{string<}.

As an example of @code{sort-subr}, here is the complete function
definition for @code{sort-lines}:

@example
@group
;; @r{Note that the first two lines of doc string}
;; @r{are effectively one line when viewed by a user.}
(defun sort-lines (reverse beg end)
  "Sort lines in region alphabetically;\
 argument means descending order.
Called from a program, there are three arguments:
@end group
@group
REVERSE (non-nil means reverse order),\
 BEG and END (region to sort).
The variable `sort-fold-case' determines\
 whether alphabetic case affects
the sort order."
@end group
@group
  (interactive "P\nr")
  (save-excursion
    (save-restriction
      (narrow-to-region beg end)
      (goto-char (point-min))
      (let ((inhibit-field-text-motion t))
        (sort-subr reverse 'forward-line 'end-of-line)))))
@end group
@end example

Here @code{forward-line} moves point to the start of the next record,
and @code{end-of-line} moves point to the end of record.  We do not pass
the arguments @var{startkeyfun} and @var{endkeyfun}, because the entire
record is used as the sort key.

The @code{sort-paragraphs} function is very much the same, except that
its @code{sort-subr} call looks like this:

@example
@group
(sort-subr reverse
           (function
            (lambda ()
              (while (and (not (eobp))
                          (looking-at paragraph-separate))
                (forward-line 1))))
           'forward-paragraph)
@end group
@end example

Markers pointing into any sort records are left with no useful
position after @code{sort-subr} returns.
@end defun

@defopt sort-fold-case
If this variable is non-@code{nil}, @code{sort-subr} and the other
buffer sorting functions ignore case when comparing strings.
@end defopt

@deffn Command sort-regexp-fields reverse record-regexp key-regexp start end
This command sorts the region between @var{start} and @var{end}
alphabetically as specified by @var{record-regexp} and @var{key-regexp}.
If @var{reverse} is a negative integer, then sorting is in reverse
order.

Alphabetical sorting means that two sort keys are compared by
comparing the first characters of each, the second characters of each,
and so on.  If a mismatch is found, it means that the sort keys are
unequal; the sort key whose character is less at the point of first
mismatch is the lesser sort key.  The individual characters are compared
according to their numerical character codes in the Emacs character set.

The value of the @var{record-regexp} argument specifies how to divide
the buffer into sort records.  At the end of each record, a search is
done for this regular expression, and the text that matches it is taken
as the next record.  For example, the regular expression @samp{^.+$},
which matches lines with at least one character besides a newline, would
make each such line into a sort record.  @xref{Regular Expressions}, for
a description of the syntax and meaning of regular expressions.

The value of the @var{key-regexp} argument specifies what part of each
record is the sort key.  The @var{key-regexp} could match the whole
record, or only a part.  In the latter case, the rest of the record has
no effect on the sorted order of records, but it is carried along when
the record moves to its new position.

The @var{key-regexp} argument can refer to the text matched by a
subexpression of @var{record-regexp}, or it can be a regular expression
on its own.

If @var{key-regexp} is:

@table @asis
@item @samp{\@var{digit}}
then the text matched by the @var{digit}th @samp{\(...\)} parenthesis
grouping in @var{record-regexp} is the sort key.

@item @samp{\&}
then the whole record is the sort key.

@item a regular expression
then @code{sort-regexp-fields} searches for a match for the regular
expression within the record.  If such a match is found, it is the sort
key.  If there is no match for @var{key-regexp} within a record then
that record is ignored, which means its position in the buffer is not
changed.  (The other records may move around it.)
@end table

For example, if you plan to sort all the lines in the region by the
first word on each line starting with the letter @samp{f}, you should
set @var{record-regexp} to @samp{^.*$} and set @var{key-regexp} to
@samp{\<f\w*\>}.  The resulting expression looks like this:

@example
@group
(sort-regexp-fields nil "^.*$" "\\<f\\w*\\>"
                    (region-beginning)
                    (region-end))
@end group
@end example

If you call @code{sort-regexp-fields} interactively, it prompts for
@var{record-regexp} and @var{key-regexp} in the minibuffer.
@end deffn

@deffn Command sort-lines reverse start end
This command alphabetically sorts lines in the region between
@var{start} and @var{end}.  If @var{reverse} is non-@code{nil}, the sort
is in reverse order.
@end deffn

@deffn Command sort-paragraphs reverse start end
This command alphabetically sorts paragraphs in the region between
@var{start} and @var{end}.  If @var{reverse} is non-@code{nil}, the sort
is in reverse order.
@end deffn

@deffn Command sort-pages reverse start end
This command alphabetically sorts pages in the region between
@var{start} and @var{end}.  If @var{reverse} is non-@code{nil}, the sort
is in reverse order.
@end deffn

@deffn Command sort-fields field start end
This command sorts lines in the region between @var{start} and
@var{end}, comparing them alphabetically by the @var{field}th field
of each line.  Fields are separated by whitespace and numbered starting
from 1.  If @var{field} is negative, sorting is by the
@w{@minus{}@var{field}th} field from the end of the line.  This command
is useful for sorting tables.
@end deffn

@deffn Command sort-numeric-fields field start end
This command sorts lines in the region between @var{start} and
@var{end}, comparing them numerically by the @var{field}th field of
each line.  Fields are separated by whitespace and numbered starting
from 1.  The specified field must contain a number in each line of the
region.  Numbers starting with 0 are treated as octal, and numbers
starting with @samp{0x} are treated as hexadecimal.

If @var{field} is negative, sorting is by the
@w{@minus{}@var{field}th} field from the end of the line.  This
command is useful for sorting tables.
@end deffn

@defopt sort-numeric-base
This variable specifies the default radix for
@code{sort-numeric-fields} to parse numbers.
@end defopt

@deffn Command sort-columns reverse &optional beg end
This command sorts the lines in the region between @var{beg} and
@var{end}, comparing them alphabetically by a certain range of
columns.  The column positions of @var{beg} and @var{end} bound the
range of columns to sort on.

If @var{reverse} is non-@code{nil}, the sort is in reverse order.

One unusual thing about this command is that the entire line
containing position @var{beg}, and the entire line containing position
@var{end}, are included in the region sorted.

Note that @code{sort-columns} rejects text that contains tabs, because
tabs could be split across the specified columns.  Use @kbd{M-x
untabify} to convert tabs to spaces before sorting.

When possible, this command actually works by calling the @code{sort}
utility program.
@end deffn

@node Columns
@section Counting Columns
@cindex columns
@cindex counting columns
@cindex horizontal position

  The column functions convert between a character position (counting
characters from the beginning of the buffer) and a column position
(counting screen characters from the beginning of a line).

  These functions count each character according to the number of
columns it occupies on the screen.  This means control characters count
as occupying 2 or 4 columns, depending upon the value of
@code{ctl-arrow}, and tabs count as occupying a number of columns that
depends on the value of @code{tab-width} and on the column where the tab
begins.  @xref{Usual Display}.

  Column number computations ignore the width of the window and the
amount of horizontal scrolling.  Consequently, a column value can be
arbitrarily high.  The first (or leftmost) column is numbered 0.  They
also ignore overlays and text properties, aside from invisibility.

@defun current-column
This function returns the horizontal position of point, measured in
columns, counting from 0 at the left margin.  The column position is the
sum of the widths of all the displayed representations of the characters
between the start of the current line and point.
@end defun

@deffn Command move-to-column column &optional force
This function moves point to @var{column} in the current line.  The
calculation of @var{column} takes into account the widths of the
displayed representations of the characters between the start of the
line and point.

When called interactively, @var{column} is the value of prefix numeric
argument.  If @var{column} is not an integer, an error is signaled.

@c This behavior used to be documented until 2013/08.
@ignore
If column @var{column} is beyond the end of the line, point moves to
the end of the line.  If @var{column} is negative, point moves to the
beginning of the line.
@end ignore

If it is impossible to move to column @var{column} because that is in
the middle of a multicolumn character such as a tab, point moves to the
end of that character.  However, if @var{force} is non-@code{nil}, and
@var{column} is in the middle of a tab, then @code{move-to-column}
either converts the tab into spaces (when @code{indent-tabs-mode} is
@code{nil}), or inserts enough spaces before it (otherwise), so that
point can move precisely to column @var{column}.  Other multicolumn
characters can cause anomalies despite @var{force}, since there is no
way to split them.

The argument @var{force} also has an effect if the line isn't long
enough to reach column @var{column}; if it is @code{t}, that means to
add whitespace at the end of the line to reach that column.

The return value is the column number actually moved to.
@end deffn

@node Indentation
@section Indentation
@cindex indentation

  The indentation functions are used to examine, move to, and change
whitespace that is at the beginning of a line.  Some of the functions
can also change whitespace elsewhere on a line.  Columns and indentation
count from zero at the left margin.

@menu
* Primitive Indent::      Functions used to count and insert indentation.
* Mode-Specific Indent::  Customize indentation for different modes.
* Region Indent::         Indent all the lines in a region.
* Relative Indent::       Indent the current line based on previous lines.
* Indent Tabs::           Adjustable, typewriter-like tab stops.
* Motion by Indent::      Move to first non-blank character.
@end menu

@node Primitive Indent
@subsection Indentation Primitives

  This section describes the primitive functions used to count and
insert indentation.  The functions in the following sections use these
primitives.  @xref{Size of Displayed Text}, for related functions.

@defun current-indentation
@comment !!Type Primitive Function
@comment !!SourceFile indent.c
This function returns the indentation of the current line, which is
the horizontal position of the first nonblank character.  If the
contents are entirely blank, then this is the horizontal position of the
end of the line.
@end defun

@deffn Command indent-to column &optional minimum
@comment !!Type Primitive Function
@comment !!SourceFile indent.c
This function indents from point with tabs and spaces until @var{column}
is reached.  If @var{minimum} is specified and non-@code{nil}, then at
least that many spaces are inserted even if this requires going beyond
@var{column}.  Otherwise the function does nothing if point is already
beyond @var{column}.  The value is the column at which the inserted
indentation ends.

The inserted whitespace characters inherit text properties from the
surrounding text (usually, from the preceding text only).  @xref{Sticky
Properties}.
@end deffn

@defopt indent-tabs-mode
@comment !!SourceFile indent.c
If this variable is non-@code{nil}, indentation functions can insert
tabs as well as spaces.  Otherwise, they insert only spaces.  Setting
this variable automatically makes it buffer-local in the current buffer.
@end defopt

@node Mode-Specific Indent
@subsection Indentation Controlled by Major Mode

  An important function of each major mode is to customize the @key{TAB}
key to indent properly for the language being edited.  This section
describes the mechanism of the @key{TAB} key and how to control it.
The functions in this section return unpredictable values.

@deffn Command indent-for-tab-command &optional rigid
This is the command bound to @key{TAB} in most editing modes.  Its
usual action is to indent the current line, but it can alternatively
insert a tab character or indent a region.

Here is what it does:

@itemize
@item
First, it checks whether Transient Mark mode is enabled and the region
is active.  If so, it called @code{indent-region} to indent all the
text in the region (@pxref{Region Indent}).

@item
Otherwise, if the indentation function in @code{indent-line-function}
is @code{indent-to-left-margin} (a trivial command that inserts a tab
character), or if the variable @code{tab-always-indent} specifies that
a tab character ought to be inserted (see below), then it inserts a
tab character.

@item
Otherwise, it indents the current line; this is done by calling the
function in @code{indent-line-function}.  If the line is already
indented, and the value of @code{tab-always-indent} is @code{complete}
(see below), it tries completing the text at point.
@end itemize

If @var{rigid} is non-@code{nil} (interactively, with a prefix
argument), then after this command indents a line or inserts a tab, it
also rigidly indents the entire balanced expression which starts at
the beginning of the current line, in order to reflect the new
indentation.  This argument is ignored if the command indents the
region.
@end deffn

@defvar indent-line-function
This variable's value is the function to be used by
@code{indent-for-tab-command}, and various other indentation commands,
to indent the current line.  It is usually assigned by the major mode;
for instance, Lisp mode sets it to @code{lisp-indent-line}, C mode
sets it to @code{c-indent-line}, and so on.  The default value is
@code{indent-relative}.  @xref{Auto-Indentation}.
@end defvar

@deffn Command indent-according-to-mode
This command calls the function in @code{indent-line-function} to
indent the current line in a way appropriate for the current major mode.
@end deffn

@deffn Command newline-and-indent
This function inserts a newline, then indents the new line (the one
following the newline just inserted) according to the major mode.  It
does indentation by calling @code{indent-according-to-mode}.
@end deffn

@deffn Command reindent-then-newline-and-indent
This command reindents the current line, inserts a newline at point,
and then indents the new line (the one following the newline just
inserted).  It does indentation on both lines by calling
@code{indent-according-to-mode}.
@end deffn

@defopt tab-always-indent
This variable can be used to customize the behavior of the @key{TAB}
(@code{indent-for-tab-command}) command.  If the value is @code{t}
(the default), the command normally just indents the current line.  If
the value is @code{nil}, the command indents the current line only if
point is at the left margin or in the line's indentation; otherwise,
it inserts a tab character.  If the value is @code{complete}, the
command first tries to indent the current line, and if the line was
already indented, it calls @code{completion-at-point} to complete the
text at point (@pxref{Completion in Buffers}).
@end defopt

@cindex literate programming
@cindex multi-mode indentation
  Some major modes need to support embedded regions of text whose
syntax belongs to a different major mode.  Examples include
@dfn{literate programming} source files that combine documentation and
snippets of source code, Yacc/Bison programs that include snippets of
Python or JS code, etc.  To correctly indent the embedded chunks, the primary
mode needs to delegate the indentation to another mode's indentation
engine (e.g., call @code{js-indent-line} for JS code or
@code{python-indent-line} for Python), while providing it with some
context to guide the indentation.  Major modes, for their part, should
avoid calling @code{widen} in their indentation code and obey
@code{prog-first-column}.

@defvar prog-indentation-context
This variable, when non-@code{nil}, holds the indentation context for
the sub-mode's indentation engine provided by the superior major mode.
The value should be a list of the form @code{(@var{first-column} . @var{rest}}.
The members of the list have the following meaning:

@table @var
@item first-column
The column to be used for top-level constructs.  This replaces the
default value of the top-level column used by the sub-mode, usually
zero.
@item rest
This value is currently unused.
@end table
@end defvar

The following convenience function should be used by major mode's
indentation engine in support of invocations as sub-modes of another
major mode.

@defun prog-first-column
Call this function instead of using a literal value (usually, zero) of
the column number for indenting top-level program constructs.  The
function's value is the column number to use for top-level constructs.
When no superior mode is in effect, this function returns zero.
@end defun


@node Region Indent
@subsection Indenting an Entire Region

  This section describes commands that indent all the lines in the
region.  They return unpredictable values.

@deffn Command indent-region start end &optional to-column
This command indents each nonblank line starting between @var{start}
(inclusive) and @var{end} (exclusive).  If @var{to-column} is
@code{nil}, @code{indent-region} indents each nonblank line by calling
the current mode's indentation function, the value of
@code{indent-line-function}.

If @var{to-column} is non-@code{nil}, it should be an integer
specifying the number of columns of indentation; then this function
gives each line exactly that much indentation, by either adding or
deleting whitespace.

If there is a fill prefix, @code{indent-region} indents each line
by making it start with the fill prefix.
@end deffn

@defvar indent-region-function
The value of this variable is a function that can be used by
@code{indent-region} as a short cut.  It should take two arguments, the
start and end of the region.  You should design the function so
that it will produce the same results as indenting the lines of the
region one by one, but presumably faster.

If the value is @code{nil}, there is no short cut, and
@code{indent-region} actually works line by line.

A short-cut function is useful in modes such as C mode and Lisp mode,
where the @code{indent-line-function} must scan from the beginning of
the function definition: applying it to each line would be quadratic in
time.  The short cut can update the scan information as it moves through
the lines indenting them; this takes linear time.  In a mode where
indenting a line individually is fast, there is no need for a short cut.

@code{indent-region} with a non-@code{nil} argument @var{to-column} has
a different meaning and does not use this variable.
@end defvar

@deffn Command indent-rigidly start end count
This function indents all lines starting between @var{start}
(inclusive) and @var{end} (exclusive) sideways by @var{count} columns.
This preserves the shape of the affected region, moving it as a
rigid unit.

This is useful not only for indenting regions of unindented text, but
also for indenting regions of formatted code.  For example, if
@var{count} is 3, this command adds 3 columns of indentation to every
line that begins in the specified region.

If called interactively with no prefix argument, this command invokes
a transient mode for adjusting indentation rigidly.  @xref{Indentation
Commands,,, emacs, The GNU Emacs Manual}.
@end deffn

@deffn Command indent-code-rigidly start end columns &optional nochange-regexp
This is like @code{indent-rigidly}, except that it doesn't alter lines
that start within strings or comments.

In addition, it doesn't alter a line if @var{nochange-regexp} matches at
the beginning of the line (if @var{nochange-regexp} is non-@code{nil}).
@end deffn

@node Relative Indent
@subsection Indentation Relative to Previous Lines

  This section describes two commands that indent the current line
based on the contents of previous lines.

@deffn Command indent-relative &optional unindented-ok
This command inserts whitespace at point, extending to the same
column as the next @dfn{indent point} of the previous nonblank line.  An
indent point is a non-whitespace character following whitespace.  The
next indent point is the first one at a column greater than the current
column of point.  For example, if point is underneath and to the left of
the first non-blank character of a line of text, it moves to that column
by inserting whitespace.

If the previous nonblank line has no next indent point (i.e., none at a
great enough column position), @code{indent-relative} either does
nothing (if @var{unindented-ok} is non-@code{nil}) or calls
@code{tab-to-tab-stop}.  Thus, if point is underneath and to the right
of the last column of a short line of text, this command ordinarily
moves point to the next tab stop by inserting whitespace.

The return value of @code{indent-relative} is unpredictable.

In the following example, point is at the beginning of the second
line:

@example
@group
            This line is indented twelve spaces.
@point{}The quick brown fox jumped.
@end group
@end example

@noindent
Evaluation of the expression @code{(indent-relative nil)} produces the
following:

@example
@group
            This line is indented twelve spaces.
            @point{}The quick brown fox jumped.
@end group
@end example

  In this next example, point is between the @samp{m} and @samp{p} of
@samp{jumped}:

@example
@group
            This line is indented twelve spaces.
The quick brown fox jum@point{}ped.
@end group
@end example

@noindent
Evaluation of the expression @code{(indent-relative nil)} produces the
following:

@example
@group
            This line is indented twelve spaces.
The quick brown fox jum  @point{}ped.
@end group
@end example
@end deffn

@deffn Command indent-relative-first-indent-point
@comment !!SourceFile indent.el
This command indents the current line like the previous nonblank line,
by calling @code{indent-relative} with @code{t} as the
@var{first-only} argument.  The return value is unpredictable.

If the previous nonblank line has no indent points beyond the current
column, this command does nothing.
@end deffn

@node Indent Tabs
@subsection Adjustable Tab Stops
@cindex tabs stops for indentation

  This section explains the mechanism for user-specified tab stops
and the mechanisms that use and set them.  The name ``tab stops'' is
used because the feature is similar to that of the tab stops on a
typewriter.  The feature works by inserting an appropriate number of
spaces and tab characters to reach the next tab stop column; it does not
affect the display of tab characters in the buffer (@pxref{Usual
Display}).  Note that the @key{TAB} character as input uses this tab
stop feature only in a few major modes, such as Text mode.
@xref{Tab Stops,,, emacs, The GNU Emacs Manual}.

@deffn Command tab-to-tab-stop
This command inserts spaces or tabs before point, up to the next tab
stop column defined by @code{tab-stop-list}.
@end deffn

@defopt tab-stop-list
This variable defines the tab stop columns used by @code{tab-to-tab-stop}.
It should be either @code{nil}, or a list of increasing integers,
which need not be evenly spaced.  The list is implicitly
extended to infinity through repetition of the interval between the
last and penultimate elements (or @code{tab-width} if the list has
fewer than two elements).  A value of @code{nil} means a tab stop
every @code{tab-width} columns.

Use @kbd{M-x edit-tab-stops} to edit the location of tab stops interactively.
@end defopt

@node Motion by Indent
@subsection Indentation-Based Motion Commands

  These commands, primarily for interactive use, act based on the
indentation in the text.

@deffn Command back-to-indentation
@comment !!SourceFile simple.el
This command moves point to the first non-whitespace character in the
current line (which is the line in which point is located).  It returns
@code{nil}.
@end deffn

@deffn Command backward-to-indentation &optional arg
@comment !!SourceFile simple.el
This command moves point backward @var{arg} lines and then to the
first nonblank character on that line.  It returns @code{nil}.
If @var{arg} is omitted or @code{nil}, it defaults to 1.
@end deffn

@deffn Command forward-to-indentation &optional arg
@comment !!SourceFile simple.el
This command moves point forward @var{arg} lines and then to the first
nonblank character on that line.  It returns @code{nil}.
If @var{arg} is omitted or @code{nil}, it defaults to 1.
@end deffn

@node Case Changes
@section Case Changes
@cindex case conversion in buffers

  The case change commands described here work on text in the current
buffer.  @xref{Case Conversion}, for case conversion functions that work
on strings and characters.  @xref{Case Tables}, for how to customize
which characters are upper or lower case and how to convert them.

@deffn Command capitalize-region start end
This function capitalizes all words in the region defined by
@var{start} and @var{end}.  To capitalize means to convert each word's
first character to upper case and convert the rest of each word to lower
case.  The function returns @code{nil}.

If one end of the region is in the middle of a word, the part of the
word within the region is treated as an entire word.

When @code{capitalize-region} is called interactively, @var{start} and
@var{end} are point and the mark, with the smallest first.

@example
@group
---------- Buffer: foo ----------
This is the contents of the 5th foo.
---------- Buffer: foo ----------
@end group

@group
(capitalize-region 1 37)
@result{} nil

---------- Buffer: foo ----------
This Is The Contents Of The 5th Foo.
---------- Buffer: foo ----------
@end group
@end example
@end deffn

@deffn Command downcase-region start end
This function converts all of the letters in the region defined by
@var{start} and @var{end} to lower case.  The function returns
@code{nil}.

When @code{downcase-region} is called interactively, @var{start} and
@var{end} are point and the mark, with the smallest first.
@end deffn

@deffn Command upcase-region start end
This function converts all of the letters in the region defined by
@var{start} and @var{end} to upper case.  The function returns
@code{nil}.

When @code{upcase-region} is called interactively, @var{start} and
@var{end} are point and the mark, with the smallest first.
@end deffn

@deffn Command capitalize-word count
This function capitalizes @var{count} words after point, moving point
over as it does.  To capitalize means to convert each word's first
character to upper case and convert the rest of each word to lower case.
If @var{count} is negative, the function capitalizes the
@minus{}@var{count} previous words but does not move point.  The value
is @code{nil}.

If point is in the middle of a word, the part of the word before point
is ignored when moving forward.  The rest is treated as an entire word.

When @code{capitalize-word} is called interactively, @var{count} is
set to the numeric prefix argument.
@end deffn

@deffn Command downcase-word count
This function converts the @var{count} words after point to all lower
case, moving point over as it does.  If @var{count} is negative, it
converts the @minus{}@var{count} previous words but does not move point.
The value is @code{nil}.

When @code{downcase-word} is called interactively, @var{count} is set
to the numeric prefix argument.
@end deffn

@deffn Command upcase-word count
This function converts the @var{count} words after point to all upper
case, moving point over as it does.  If @var{count} is negative, it
converts the @minus{}@var{count} previous words but does not move point.
The value is @code{nil}.

When @code{upcase-word} is called interactively, @var{count} is set to
the numeric prefix argument.
@end deffn

@node Text Properties
@section Text Properties
@cindex text properties
@cindex attributes of text
@cindex properties of text

  Each character position in a buffer or a string can have a @dfn{text
property list}, much like the property list of a symbol (@pxref{Property
Lists}).  The properties belong to a particular character at a
particular place, such as, the letter @samp{T} at the beginning of this
sentence or the first @samp{o} in @samp{foo}---if the same character
occurs in two different places, the two occurrences in general have
different properties.

  Each property has a name and a value.  Both of these can be any Lisp
object, but the name is normally a symbol.  Typically each property
name symbol is used for a particular purpose; for instance, the text
property @code{face} specifies the faces for displaying the character
(@pxref{Special Properties}).  The usual way to access the property
list is to specify a name and ask what value corresponds to it.

  If a character has a @code{category} property, we call it the
@dfn{property category} of the character.  It should be a symbol.  The
properties of the symbol serve as defaults for the properties of the
character.

  Copying text between strings and buffers preserves the properties
along with the characters; this includes such diverse functions as
@code{substring}, @code{insert}, and @code{buffer-substring}.

@menu
* Examining Properties::   Looking at the properties of one character.
* Changing Properties::    Setting the properties of a range of text.
* Property Search::        Searching for where a property changes value.
* Special Properties::     Particular properties with special meanings.
* Format Properties::      Properties for representing formatting of text.
* Sticky Properties::      How inserted text gets properties from
                             neighboring text.
* Lazy Properties::        Computing text properties in a lazy fashion
                             only when text is examined.
* Clickable Text::         Using text properties to make regions of text
                             do something when you click on them.
* Fields::                 The @code{field} property defines
                             fields within the buffer.
* Not Intervals::          Why text properties do not use
                             Lisp-visible text intervals.
@end menu

@node Examining Properties
@subsection Examining Text Properties
@cindex examining text properties
@cindex text properties, examining

  The simplest way to examine text properties is to ask for the value of
a particular property of a particular character.  For that, use
@code{get-text-property}.  Use @code{text-properties-at} to get the
entire property list of a character.  @xref{Property Search}, for
functions to examine the properties of a number of characters at once.

  These functions handle both strings and buffers.  Keep in mind that
positions in a string start from 0, whereas positions in a buffer start
from 1.

@defun get-text-property pos prop &optional object
This function returns the value of the @var{prop} property of the
character after position @var{pos} in @var{object} (a buffer or
string).  The argument @var{object} is optional and defaults to the
current buffer.

If there is no @var{prop} property strictly speaking, but the character
has a property category that is a symbol, then @code{get-text-property} returns
the @var{prop} property of that symbol.
@end defun

@defun get-char-property position prop &optional object
This function is like @code{get-text-property}, except that it checks
overlays first and then text properties.  @xref{Overlays}.

The argument @var{object} may be a string, a buffer, or a window.  If
it is a window, then the buffer displayed in that window is used for
text properties and overlays, but only the overlays active for that
window are considered.  If @var{object} is a buffer, then overlays in
that buffer are considered first, in order of decreasing priority,
followed by the text properties.  If @var{object} is a string, only
text properties are considered, since strings never have overlays.
@end defun

@defun get-pos-property position prop &optional object
This function is like @code{get-char-property}, except that it pays
attention to properties' stickiness and overlays' advancement settings
instead of the property of the character at (i.e., right after)
@var{position}.
@end defun

@defun get-char-property-and-overlay position prop &optional object
This is like @code{get-char-property}, but gives extra information
about the overlay that the property value comes from.

Its value is a cons cell whose @sc{car} is the property value, the
same value @code{get-char-property} would return with the same
arguments.  Its @sc{cdr} is the overlay in which the property was
found, or @code{nil}, if it was found as a text property or not found
at all.

If @var{position} is at the end of @var{object}, both the @sc{car} and
the @sc{cdr} of the value are @code{nil}.
@end defun

@defvar char-property-alias-alist
This variable holds an alist which maps property names to a list of
alternative property names.  If a character does not specify a direct
value for a property, the alternative property names are consulted in
order; the first non-@code{nil} value is used.  This variable takes
precedence over @code{default-text-properties}, and @code{category}
properties take precedence over this variable.
@end defvar

@defun text-properties-at position &optional object
This function returns the entire property list of the character at
@var{position} in the string or buffer @var{object}.  If @var{object} is
@code{nil}, it defaults to the current buffer.
@end defun

@defvar default-text-properties
This variable holds a property list giving default values for text
properties.  Whenever a character does not specify a value for a
property, neither directly, through a category symbol, or through
@code{char-property-alias-alist}, the value stored in this list is
used instead.  Here is an example:

@example
(setq default-text-properties '(foo 69)
      char-property-alias-alist nil)
;; @r{Make sure character 1 has no properties of its own.}
(set-text-properties 1 2 nil)
;; @r{What we get, when we ask, is the default value.}
(get-text-property 1 'foo)
     @result{} 69
@end example
@end defvar

@node Changing Properties
@subsection Changing Text Properties
@cindex changing text properties
@cindex text properties, changing

  The primitives for changing properties apply to a specified range of
text in a buffer or string.  The function @code{set-text-properties}
(see end of section) sets the entire property list of the text in that
range; more often, it is useful to add, change, or delete just certain
properties specified by name.

  Since text properties are considered part of the contents of the
buffer (or string), and can affect how a buffer looks on the screen,
any change in buffer text properties marks the buffer as modified.
Buffer text property changes are undoable also (@pxref{Undo}).
Positions in a string start from 0, whereas positions in a buffer
start from 1.

@defun put-text-property start end prop value &optional object
This function sets the @var{prop} property to @var{value} for the text
between @var{start} and @var{end} in the string or buffer @var{object}.
If @var{object} is @code{nil}, it defaults to the current buffer.
@end defun

@defun add-text-properties start end props &optional object
This function adds or overrides text properties for the text between
@var{start} and @var{end} in the string or buffer @var{object}.  If
@var{object} is @code{nil}, it defaults to the current buffer.

The argument @var{props} specifies which properties to add.  It should
have the form of a property list (@pxref{Property Lists}): a list whose
elements include the property names followed alternately by the
corresponding values.

The return value is @code{t} if the function actually changed some
property's value; @code{nil} otherwise (if @var{props} is @code{nil} or
its values agree with those in the text).

For example, here is how to set the @code{comment} and @code{face}
properties of a range of text:

@example
(add-text-properties @var{start} @var{end}
                     '(comment t face highlight))
@end example
@end defun

@defun remove-text-properties start end props &optional object
This function deletes specified text properties from the text between
@var{start} and @var{end} in the string or buffer @var{object}.  If
@var{object} is @code{nil}, it defaults to the current buffer.

The argument @var{props} specifies which properties to delete.  It
should have the form of a property list (@pxref{Property Lists}): a list
whose elements are property names alternating with corresponding values.
But only the names matter---the values that accompany them are ignored.
For example, here's how to remove the @code{face} property.

@example
(remove-text-properties @var{start} @var{end} '(face nil))
@end example

The return value is @code{t} if the function actually changed some
property's value; @code{nil} otherwise (if @var{props} is @code{nil} or
if no character in the specified text had any of those properties).

To remove all text properties from certain text, use
@code{set-text-properties} and specify @code{nil} for the new property
list.
@end defun

@defun remove-list-of-text-properties start end list-of-properties &optional object
Like @code{remove-text-properties} except that
@var{list-of-properties} is a list of property names only, not an
alternating list of property names and values.
@end defun

@defun set-text-properties start end props &optional object
This function completely replaces the text property list for the text
between @var{start} and @var{end} in the string or buffer @var{object}.
If @var{object} is @code{nil}, it defaults to the current buffer.

The argument @var{props} is the new property list.  It should be a list
whose elements are property names alternating with corresponding values.

After @code{set-text-properties} returns, all the characters in the
specified range have identical properties.

If @var{props} is @code{nil}, the effect is to get rid of all properties
from the specified range of text.  Here's an example:

@example
(set-text-properties @var{start} @var{end} nil)
@end example

Do not rely on the return value of this function.
@end defun

@defun add-face-text-property start end face &optional appendp object
This function acts on the text between @var{start} and @var{end},
adding the face @var{face} to the @code{face} text property.
@var{face} should be a valid value for the @code{face} property
(@pxref{Special Properties}), such as a face name or an anonymous face
(@pxref{Faces}).

If any text in the region already has a non-@code{nil} @code{face} property,
those face(s) are retained.  This function sets the @code{face}
property to a list of faces, with @var{face} as the first element (by
default) and the pre-existing faces as the remaining elements.  If the
optional argument @var{appendp} is non-@code{nil}, @var{face} is
appended to the end of the list instead.  Note that in a face list,
the first occurring value for each attribute takes precedence.

For example, the following code would assign an italicized green face
to the text between @var{start} and @var{end}:

@example
(add-face-text-property @var{start} @var{end} 'italic)
(add-face-text-property @var{start} @var{end} '(:foreground "red"))
(add-face-text-property @var{start} @var{end} '(:foreground "green"))
@end example

The optional argument @var{object}, if non-@code{nil}, specifies a
buffer or string to act on, rather than the current buffer.  If
@var{object} is a string, then @var{start} and @var{end} are
zero-based indices into the string.
@end defun

  The easiest way to make a string with text properties is with
@code{propertize}:

@defun propertize string &rest properties
This function returns a copy of @var{string} with the text properties
@var{properties} added.  These properties apply to all the characters
in the string that is returned.  Here is an example that constructs a
string with a @code{face} property and a @code{mouse-face} property:

@smallexample
(propertize "foo" 'face 'italic
            'mouse-face 'bold-italic)
     @result{} #("foo" 0 3 (mouse-face bold-italic face italic))
@end smallexample

To put different properties on various parts of a string, you can
construct each part with @code{propertize} and then combine them with
@code{concat}:

@smallexample
(concat
 (propertize "foo" 'face 'italic
             'mouse-face 'bold-italic)
 " and "
 (propertize "bar" 'face 'italic
             'mouse-face 'bold-italic))
     @result{} #("foo and bar"
                 0 3 (face italic mouse-face bold-italic)
                 3 8 nil
                 8 11 (face italic mouse-face bold-italic))
@end smallexample
@end defun

  @xref{Buffer Contents}, for the function
@code{buffer-substring-no-properties}, which copies text from the
buffer but does not copy its properties.

@findex with-silent-modifications
  If you wish to add text properties to a buffer or remove them
without marking the buffer as modified, you can wrap the calls above
in the @code{with-silent-modifications} macro.  @xref{Buffer
Modification}.

@node Property Search
@subsection Text Property Search Functions
@cindex searching text properties
@cindex text properties, searching

  In typical use of text properties, most of the time several or many
consecutive characters have the same value for a property.  Rather than
writing your programs to examine characters one by one, it is much
faster to process chunks of text that have the same property value.

  Here are functions you can use to do this.  They use @code{eq} for
comparing property values.  In all cases, @var{object} defaults to the
current buffer.

  For good performance, it's very important to use the @var{limit}
argument to these functions, especially the ones that search for a
single property---otherwise, they may spend a long time scanning to the
end of the buffer, if the property you are interested in does not change.

  These functions do not move point; instead, they return a position (or
@code{nil}).  Remember that a position is always between two characters;
the position returned by these functions is between two characters with
different properties.

@defun next-property-change pos &optional object limit
The function scans the text forward from position @var{pos} in the
string or buffer @var{object} until it finds a change in some text
property, then returns the position of the change.  In other words, it
returns the position of the first character beyond @var{pos} whose
properties are not identical to those of the character just after
@var{pos}.

If @var{limit} is non-@code{nil}, then the scan ends at position
@var{limit}.  If there is no property change before that point, this
function returns @var{limit}.

The value is @code{nil} if the properties remain unchanged all the way
to the end of @var{object} and @var{limit} is @code{nil}.  If the value
is non-@code{nil}, it is a position greater than or equal to @var{pos}.
The value equals @var{pos} only when @var{limit} equals @var{pos}.

Here is an example of how to scan the buffer by chunks of text within
which all properties are constant:

@smallexample
(while (not (eobp))
  (let ((plist (text-properties-at (point)))
        (next-change
         (or (next-property-change (point) (current-buffer))
             (point-max))))
    @r{Process text from point to @var{next-change}@dots{}}
    (goto-char next-change)))
@end smallexample
@end defun

@defun previous-property-change pos &optional object limit
This is like @code{next-property-change}, but scans back from @var{pos}
instead of forward.  If the value is non-@code{nil}, it is a position
less than or equal to @var{pos}; it equals @var{pos} only if @var{limit}
equals @var{pos}.
@end defun

@defun next-single-property-change pos prop &optional object limit
The function scans text for a change in the @var{prop} property, then
returns the position of the change.  The scan goes forward from
position @var{pos} in the string or buffer @var{object}.  In other
words, this function returns the position of the first character
beyond @var{pos} whose @var{prop} property differs from that of the
character just after @var{pos}.

If @var{limit} is non-@code{nil}, then the scan ends at position
@var{limit}.  If there is no property change before that point,
@code{next-single-property-change} returns @var{limit}.

The value is @code{nil} if the property remains unchanged all the way to
the end of @var{object} and @var{limit} is @code{nil}.  If the value is
non-@code{nil}, it is a position greater than or equal to @var{pos}; it
equals @var{pos} only if @var{limit} equals @var{pos}.
@end defun

@defun previous-single-property-change pos prop &optional object limit
This is like @code{next-single-property-change}, but scans back from
@var{pos} instead of forward.  If the value is non-@code{nil}, it is a
position less than or equal to @var{pos}; it equals @var{pos} only if
@var{limit} equals @var{pos}.
@end defun

@defun next-char-property-change pos &optional limit
This is like @code{next-property-change} except that it considers
overlay properties as well as text properties, and if no change is
found before the end of the buffer, it returns the maximum buffer
position rather than @code{nil} (in this sense, it resembles the
corresponding overlay function @code{next-overlay-change}, rather than
@code{next-property-change}).  There is no @var{object} operand
because this function operates only on the current buffer.  It returns
the next address at which either kind of property changes.
@end defun

@defun previous-char-property-change pos &optional limit
This is like @code{next-char-property-change}, but scans back from
@var{pos} instead of forward, and returns the minimum buffer
position if no change is found.
@end defun

@defun next-single-char-property-change pos prop &optional object limit
This is like @code{next-single-property-change} except that it
considers overlay properties as well as text properties, and if no
change is found before the end of the @var{object}, it returns the
maximum valid position in @var{object} rather than @code{nil}.  Unlike
@code{next-char-property-change}, this function @emph{does} have an
@var{object} operand; if @var{object} is not a buffer, only
text-properties are considered.
@end defun

@defun previous-single-char-property-change pos prop &optional object limit
This is like @code{next-single-char-property-change}, but scans back
from @var{pos} instead of forward, and returns the minimum valid
position in @var{object} if no change is found.
@end defun

@defun text-property-any start end prop value &optional object
This function returns non-@code{nil} if at least one character between
@var{start} and @var{end} has a property @var{prop} whose value is
@var{value}.  More precisely, it returns the position of the first such
character.  Otherwise, it returns @code{nil}.

The optional fifth argument, @var{object}, specifies the string or
buffer to scan.  Positions are relative to @var{object}.  The default
for @var{object} is the current buffer.
@end defun

@defun text-property-not-all start end prop value &optional object
This function returns non-@code{nil} if at least one character between
@var{start} and @var{end} does not have a property @var{prop} with value
@var{value}.  More precisely, it returns the position of the first such
character.  Otherwise, it returns @code{nil}.

The optional fifth argument, @var{object}, specifies the string or
buffer to scan.  Positions are relative to @var{object}.  The default
for @var{object} is the current buffer.
@end defun

@defun text-property-search-forward prop &optional value predicate not-current
Search for the next region that has text property @var{prop} set to
@var{value} according to @var{predicate}.

This function is modelled after @code{search-forward} and friends in
that it moves point, but it returns a structure that describes the
match instead of returning it in @code{match-beginning} and friends.

If the text property can't be found, the function returns @code{nil}.
If it's found, point is placed at the end of the region that has this
text property match, and a @code{prop-match} structure is returned.

@var{predicate} can either be @code{t} (which is a synonym for
@code{equal}), @code{nil} (which means ``not equal''), or a predicate
that will be called with two parameters: The first is @var{value}, and
the second is the value of the text property we're inspecting.

If @var{not-current}, if point is in a region where we have a match,
then skip past that and find the next instance instead.

The @code{prop-match} structure has the following accessors:
@code{prop-match-beginning} (the start of the match),
@code{prop-match-end} (the end of the match), and
@code{prop-match-value} (the value of @var{property} at the start of
the match).

In the examples below, imagine that you're in a buffer that looks like
this:

@example
This is a bold and here's bolditalic and this is the end.
@end example

That is, the ``bold'' words are the @code{bold} face, and the
``italic'' word is in the @code{italic} face.

With point at the start:

@lisp
(while (setq match (text-property-search-forward 'face 'bold t))
  (push (buffer-substring (prop-match-beginning match)
                          (prop-match-end match))
        words))
@end lisp

This will pick out all the words that use the @code{bold} face.

@lisp
(while (setq match (text-property-search-forward 'face nil t))
  (push (buffer-substring (prop-match-beginning match)
                          (prop-match-end match))
        words))
@end lisp

This will pick out all the bits that have no face properties, which
will result in the list @samp{("This is a " "and here's " "and this is
the end")} (only reversed, since we used @code{push}).

@lisp
(while (setq match (text-property-search-forward 'face nil nil))
  (push (buffer-substring (prop-match-beginning match)
                          (prop-match-end match))
        words))
@end lisp

This will pick out all the regions where @code{face} is set to
something, but this is split up into where the properties change, so
the result here will be @samp{("bold" "bold" "italic")}.

For a more realistic example where you might use this, consider that
you have a buffer where certain sections represent URLs, and these are
tagged with @code{shr-url}.

@lisp
(while (setq match (text-property-search-forward 'shr-url nil nil))
  (push (prop-match-value match) urls))
@end lisp

This will give you a list of all those URLs.

@end defun

@defun text-property-search-backward prop &optional value predicate not-current
This is just like @code{text-property-search-backward}, but searches
backward instead.  Point is placed at the beginning of the matched
region instead of the end, though.
@end defun


@node Special Properties
@subsection Properties with Special Meanings

  Here is a table of text property names that have special built-in
meanings.  The following sections list a few additional special property
names that control filling and property inheritance.  All other names
have no standard meaning, and you can use them as you like.

  Note: the properties @code{composition}, @code{display},
@code{invisible} and @code{intangible} can also cause point to move to
an acceptable place, after each Emacs command.  @xref{Adjusting
Point}.

@table @code
@cindex property category of text character
@c FIXME: Isn't @kindex for keyboard commands?
@kindex category @r{(text property)}
@item category
If a character has a @code{category} property, we call it the
@dfn{property category} of the character.  It should be a symbol.  The
properties of this symbol serve as defaults for the properties of the
character.

@item face
@cindex face codes of text
@kindex face @r{(text property)}
The @code{face} property controls the appearance of the character
(@pxref{Faces}).  The value of the property can be the following:

@itemize @bullet
@item
A face name (a symbol or string).

@item
An anonymous face: a property list of the form @code{(@var{keyword}
@var{value} @dots{})}, where each @var{keyword} is a face attribute
name and @var{value} is a value for that attribute.

@item
A list of faces.  Each list element should be either a face name or an
anonymous face.  This specifies a face which is an aggregate of the
attributes of each of the listed faces.  Faces occurring earlier in
the list have higher priority.

@item
A cons cell of the form @code{(foreground-color . @var{color-name})}
or @code{(background-color . @var{color-name})}.  This specifies the
foreground or background color, similar to @code{(:foreground
@var{color-name})} or @code{(:background @var{color-name})}.  This
form is supported for backward compatibility only, and should be
avoided.

@item
A cons cell of the form @w{@code{(:filtered @var{filter}
@var{face-spec})}}, that specifies the face given by @var{face-spec},
but only if @var{filter} matches when the face is used for display.
The @var{face-spec} can use any of the forms mentioned above.  The
@var{filter} should be of the form @w{@code{(:window @var{param}
@var{value})}}, which matches for windows whose parameter @var{param}
is @code{eq} to @var{value}.  If the variable
@code{face-filters-always-match} is non-@code{nil}, all face filters
are deemed to have matched.
@end itemize

Font Lock mode (@pxref{Font Lock Mode}) works in most buffers by
dynamically updating the @code{face} property of characters based on
the context.

The @code{add-face-text-property} function provides a convenient way
to set this text property.  @xref{Changing Properties}.

@item font-lock-face
@kindex font-lock-face @r{(text property)}
This property specifies a value for the @code{face} property that Font
Lock mode should apply to the underlying text.  It is one of the
fontification methods used by Font Lock mode, and is useful for
special modes that implement their own highlighting.
@xref{Precalculated Fontification}.  When Font Lock mode is disabled,
@code{font-lock-face} has no effect.

@item mouse-face
@kindex mouse-face @r{(text property)}
This property is used instead of @code{face} when the mouse is on or
near the character.  For this purpose, ``near'' means that all text
between the character and where the mouse is have the same
@code{mouse-face} property value.

Emacs ignores all face attributes from the @code{mouse-face} property
that alter the text size (e.g., @code{:height}, @code{:weight}, and
@code{:slant}).  Those attributes are always the same as for the
unhighlighted text.

@item fontified
@kindex fontified @r{(text property)}
This property says whether the text is ready for display.  If
@code{nil}, Emacs's redisplay routine calls the functions in
@code{fontification-functions} (@pxref{Auto Faces}) to prepare this
part of the buffer before it is displayed.  It is used internally by
the just-in-time font locking code.

@item display
This property activates various features that change the
way text is displayed.  For example, it can make text appear taller
or shorter, higher or lower, wider or narrow, or replaced with an image.
@xref{Display Property}.

@item help-echo
@kindex help-echo @r{(text property)}
@cindex tooltip for help strings
@anchor{Text help-echo}
If text has a string as its @code{help-echo} property, then when you
move the mouse onto that text, Emacs displays that string in the echo
area, or in the tooltip window (@pxref{Tooltips}).

If the value of the @code{help-echo} property is a function, that
function is called with three arguments, @var{window}, @var{object} and
@var{pos} and should return a help string or @code{nil} for
none.  The first argument, @var{window} is the window in which
the help was found.  The second, @var{object}, is the buffer, overlay or
string which had the @code{help-echo} property.  The @var{pos}
argument is as follows:

@itemize @bullet{}
@item
If @var{object} is a buffer, @var{pos} is the position in the buffer.
@item
If @var{object} is an overlay, that overlay has a @code{help-echo}
property, and @var{pos} is the position in the overlay's buffer.
@item
If @var{object} is a string (an overlay string or a string displayed
with the @code{display} property), @var{pos} is the position in that
string.
@end itemize

If the value of the @code{help-echo} property is neither a function nor
a string, it is evaluated to obtain a help string.

You can alter the way help text is displayed by setting the variable
@code{show-help-function} (@pxref{Help display}).

This feature is used in the mode line and for other active text.

@item keymap
@cindex keymap of character
@kindex keymap @r{(text property)}
The @code{keymap} property specifies an additional keymap for
commands.  When this keymap applies, it is used for key lookup before
the minor mode keymaps and before the buffer's local map.
@xref{Active Keymaps}.  If the property value is a symbol, the
symbol's function definition is used as the keymap.

The property's value for the character before point applies if it is
non-@code{nil} and rear-sticky, and the property's value for the
character after point applies if it is non-@code{nil} and
front-sticky.  (For mouse clicks, the position of the click is used
instead of the position of point.)

@item local-map
@kindex local-map @r{(text property)}
This property works like @code{keymap} except that it specifies a
keymap to use @emph{instead of} the buffer's local map.  For most
purposes (perhaps all purposes), it is better to use the @code{keymap}
property.

@item syntax-table
The @code{syntax-table} property overrides what the syntax table says
about this particular character.  @xref{Syntax Properties}.

@item read-only
@cindex read-only character
@kindex read-only @r{(text property)}
If a character has the property @code{read-only}, then modifying that
character is not allowed.  Any command that would do so gets an error,
@code{text-read-only}.  If the property value is a string, that string
is used as the error message.

Insertion next to a read-only character is an error if inserting
ordinary text there would inherit the @code{read-only} property due to
stickiness.  Thus, you can control permission to insert next to
read-only text by controlling the stickiness.  @xref{Sticky Properties}.

Since changing properties counts as modifying the buffer, it is not
possible to remove a @code{read-only} property unless you know the
special trick: bind @code{inhibit-read-only} to a non-@code{nil} value
and then remove the property.  @xref{Read Only Buffers}.

@item inhibit-read-only
@kindex inhibit-read-only @r{(text property)}
Characters that have the property @code{inhibit-read-only} can be
edited even in read-only buffers.  @xref{Read Only Buffers}.

@item invisible
@kindex invisible @r{(text property)}
A non-@code{nil} @code{invisible} property can make a character invisible
on the screen.  @xref{Invisible Text}, for details.

@item intangible
@kindex intangible @r{(text property)}
If a group of consecutive characters have equal and non-@code{nil}
@code{intangible} properties, then you cannot place point between them.
If you try to move point forward into the group, point actually moves to
the end of the group.  If you try to move point backward into the group,
point actually moves to the start of the group.

If consecutive characters have unequal non-@code{nil}
@code{intangible} properties, they belong to separate groups; each
group is separately treated as described above.

When the variable @code{inhibit-point-motion-hooks} is non-@code{nil}
(as it is by default), the @code{intangible} property is ignored.

Beware: this property operates at a very low level, and affects a lot of code
in unexpected ways.  So use it with extreme caution.  A common misuse is to put
an intangible property on invisible text, which is actually unnecessary since
the command loop will move point outside of the invisible text at the end of
each command anyway.  @xref{Adjusting Point}.  For these reasons, this
property is obsolete; use the @code{cursor-intangible} property instead.

@item cursor-intangible
@kindex cursor-intangible @r{(text property)}
@findex cursor-intangible-mode
When the minor mode @code{cursor-intangible-mode} is turned on, point
is moved away from any position that has a non-@code{nil}
@code{cursor-intangible} property, just before redisplay happens.

@vindex cursor-sensor-inhibit
When the variable @code{cursor-sensor-inhibit} is non-@code{nil}, the
@code{cursor-intangible} property and the
@code{cursor-sensor-functions} property (described below) are ignored.

@item field
@kindex field @r{(text property)}
Consecutive characters with the same @code{field} property constitute a
@dfn{field}.  Some motion functions including @code{forward-word} and
@code{beginning-of-line} stop moving at a field boundary.
@xref{Fields}.

@item cursor
@kindex cursor @r{(text property)}
Normally, the cursor is displayed at the beginning or the end of any
overlay and text property strings present at the current buffer
position.  You can place the cursor on any desired character of these
strings by giving that character a non-@code{nil} @code{cursor} text
property.  In addition, if the value of the @code{cursor} property is
an integer, it specifies the number of buffer's character
positions, starting with the position where the overlay or the
@code{display} property begins, for which the cursor should be
displayed on that character.  Specifically, if the value of the
@code{cursor} property of a character is the number @var{n}, the
cursor will be displayed on this character for any buffer position in
the range @code{[@var{ovpos}..@var{ovpos}+@var{n})}, where @var{ovpos}
is the overlay's starting position given by @code{overlay-start}
(@pxref{Managing Overlays}), or the position where the @code{display}
text property begins in the buffer.

In other words, the string character with the @code{cursor} property
of any non-@code{nil} value is the character where to display the
cursor.  The value of the property says for which buffer positions to
display the cursor there.  If the value is an integer @var{n},
the cursor is displayed there when point is anywhere between the
beginning of the overlay or @code{display} property and @var{n}
positions after that.  If the value is anything else and
non-@code{nil}, the cursor is displayed there only when point is at
the beginning of the @code{display} property or at
@code{overlay-start}.

@cindex cursor position for @code{display} properties and overlays
When the buffer has many overlay strings (e.g., @pxref{Overlay
Properties, before-string}) that conceal some of the buffer text or
@code{display} properties that are strings, it is a good idea to use
the @code{cursor} property on these strings to cue the Emacs display
about the places where to put the cursor while traversing these
strings.  This directly communicates to the display engine where the
Lisp program wants to put the cursor, or where the user would expect
the cursor, when point is located on some buffer position that is
``covered'' by the display or overlay string.

@item pointer
@kindex pointer @r{(text property)}
This specifies a specific pointer shape when the mouse pointer is over
this text or image.  @xref{Pointer Shape}, for possible pointer
shapes.

@item line-spacing
@kindex line-spacing @r{(text property)}
A newline can have a @code{line-spacing} text or overlay property that
controls the height of the display line ending with that newline.  The
property value overrides the default frame line spacing and the buffer
local @code{line-spacing} variable.  @xref{Line Height}.

@item line-height
@kindex line-height @r{(text property)}
A newline can have a @code{line-height} text or overlay property that
controls the total height of the display line ending in that newline.
@xref{Line Height}.

@item wrap-prefix
If text has a @code{wrap-prefix} property, the prefix it defines will
be added at display time to the beginning of every continuation line
due to text wrapping (so if lines are truncated, the wrap-prefix is
never used).  It may be a string or an image (@pxref{Other Display
Specs}), or a stretch of whitespace such as specified by the
@code{:width} or @code{:align-to} display properties (@pxref{Specified
Space}).

A wrap-prefix may also be specified for an entire buffer using the
@code{wrap-prefix} buffer-local variable (however, a
@code{wrap-prefix} text-property takes precedence over the value of
the @code{wrap-prefix} variable).  @xref{Truncation}.

@item line-prefix
If text has a @code{line-prefix} property, the prefix it defines will
be added at display time to the beginning of every non-continuation
line.  It may be a string or an image (@pxref{Other Display
Specs}), or a stretch of whitespace such as specified by the
@code{:width} or @code{:align-to} display properties (@pxref{Specified
Space}).

A line-prefix may also be specified for an entire buffer using the
@code{line-prefix} buffer-local variable (however, a
@code{line-prefix} text-property takes precedence over the value of
the @code{line-prefix} variable).  @xref{Truncation}.

@item modification-hooks
@cindex change hooks for a character
@cindex hooks for changing a character
@kindex modification-hooks @r{(text property)}
If a character has the property @code{modification-hooks}, then its
value should be a list of functions; modifying that character calls
all of those functions before the actual modification.  Each function
receives two arguments: the beginning and end of the part of the
buffer being modified.  Note that if a particular modification hook
function appears on several characters being modified by a single
primitive, you can't predict how many times the function will
be called.
Furthermore, insertion will not modify any existing character, so this
hook will only be run when removing some characters, replacing them
with others, or changing their text-properties.

If these functions modify the buffer, they should bind
@code{inhibit-modification-hooks} to @code{t} around doing so, to
avoid confusing the internal mechanism that calls these hooks.

Overlays also support the @code{modification-hooks} property, but the
details are somewhat different (@pxref{Overlay Properties}).

@item insert-in-front-hooks
@itemx insert-behind-hooks
@kindex insert-in-front-hooks @r{(text property)}
@kindex insert-behind-hooks @r{(text property)}
The operation of inserting text in a buffer also calls the functions
listed in the @code{insert-in-front-hooks} property of the following
character and in the @code{insert-behind-hooks} property of the
preceding character.  These functions receive two arguments, the
beginning and end of the inserted text.  The functions are called
@emph{after} the actual insertion takes place.

See also @ref{Change Hooks}, for other hooks that are called
when you change text in a buffer.

@item point-entered
@itemx point-left
@cindex hooks for motion of point
@kindex point-entered @r{(text property)}
@kindex point-left @r{(text property)}
The special properties @code{point-entered} and @code{point-left}
record hook functions that report motion of point.  Each time point
moves, Emacs compares these two property values:

@itemize @bullet
@item
the @code{point-left} property of the character after the old location,
and
@item
the @code{point-entered} property of the character after the new
location.
@end itemize

@noindent
If these two values differ, each of them is called (if not @code{nil})
with two arguments: the old value of point, and the new one.

The same comparison is made for the characters before the old and new
locations.  The result may be to execute two @code{point-left} functions
(which may be the same function) and/or two @code{point-entered}
functions (which may be the same function).  In any case, all the
@code{point-left} functions are called first, followed by all the
@code{point-entered} functions.

It is possible to use @code{char-after} to examine characters at various
buffer positions without moving point to those positions.  Only an
actual change in the value of point runs these hook functions.

The variable @code{inhibit-point-motion-hooks} by default inhibits
running the @code{point-left} and @code{point-entered} hooks, see
@ref{Inhibit point motion hooks}.

These properties are obsolete; please use
@code{cursor-sensor-functions} instead.

@item cursor-sensor-functions
@kindex cursor-sensor-functions @r{(text property)}
@findex cursor-sensor-mode
This special property records a list of functions that react to cursor
motion.  Each function in the list is called, just before redisplay,
with 3 arguments: the affected window, the previous known position of
the cursor, and one of the symbols @code{entered} or @code{left},
depending on whether the cursor is entering the text that has this
property or leaving it.  The functions are called only when the minor
mode @code{cursor-sensor-mode} is turned on.

When the variable @code{cursor-sensor-inhibit} is non-@code{nil}, the
@code{cursor-sensor-functions} property is ignored.

@item composition
@kindex composition @r{(text property)}
This text property is used to display a sequence of characters as a
single glyph composed from components.  But the value of the property
itself is completely internal to Emacs and should not be manipulated
directly by, for instance, @code{put-text-property}.

@end table

@defvar inhibit-point-motion-hooks
@anchor{Inhibit point motion hooks} When this obsolete variable is
non-@code{nil}, @code{point-left} and @code{point-entered} hooks are
not run, and the @code{intangible} property has no effect.  Do not set
this variable globally; bind it with @code{let}.  Since the affected
properties are obsolete, this variable's default value is @code{t}, to
effectively disable them.
@end defvar

@defvar show-help-function
@anchor{Help display} If this variable is non-@code{nil}, it specifies a
function called to display help strings.  These may be @code{help-echo}
properties, menu help strings (@pxref{Simple Menu Items},
@pxref{Extended Menu Items}), or tool bar help strings (@pxref{Tool
Bar}).  The specified function is called with one argument, the help
string to display, which is passed through
@code{substitute-command-keys} before being given to the function; see
@ref{Keys in Documentation}.  Tooltip mode (@pxref{Tooltips,,, emacs,
The GNU Emacs Manual}) provides an example.
@end defvar

@defvar face-filters-always-match
If this variable is non-@code{nil}, face filters that specify
attributes applied only when certain conditions are met will be deemed
to match always.
@end defvar

@node Format Properties
@subsection Formatted Text Properties

  These text properties affect the behavior of the fill commands.  They
are used for representing formatted text.  @xref{Filling}, and
@ref{Margins}.

@table @code
@item hard
If a newline character has this property, it is a ``hard'' newline.
The fill commands do not alter hard newlines and do not move words
across them.  However, this property takes effect only if the
@code{use-hard-newlines} minor mode is enabled.  @xref{Hard and Soft
Newlines,, Hard and Soft Newlines, emacs, The GNU Emacs Manual}.

@item right-margin
This property specifies an extra right margin for filling this part of the
text.

@item left-margin
This property specifies an extra left margin for filling this part of the
text.

@item justification
This property specifies the style of justification for filling this part
of the text.
@end table

@node Sticky Properties
@subsection Stickiness of Text Properties
@cindex sticky text properties
@cindex inheritance, text property

  Self-inserting characters, the ones that get inserted into a buffer
when the user types them (@pxref{Commands for Insertion}), normally
take on the same properties as the preceding character.  This is
called @dfn{inheritance} of properties.

  By contrast, a Lisp program can do insertion with inheritance or without,
depending on the choice of insertion primitive.  The ordinary text
insertion functions, such as @code{insert}, do not inherit any
properties.  They insert text with precisely the properties of the
string being inserted, and no others.  This is correct for programs
that copy text from one context to another---for example, into or out
of the kill ring.  To insert with inheritance, use the special
primitives described in this section.  Self-inserting characters
inherit properties because they work using these primitives.

  When you do insertion with inheritance, @emph{which} properties are
inherited, and from where, depends on which properties are @dfn{sticky}.
Insertion after a character inherits those of its properties that are
@dfn{rear-sticky}.  Insertion before a character inherits those of its
properties that are @dfn{front-sticky}.  When both sides offer different
sticky values for the same property, the previous character's value
takes precedence.

  By default, a text property is rear-sticky but not front-sticky; thus,
the default is to inherit all the properties of the preceding character,
and nothing from the following character.

  You can control the stickiness of various text properties with two
specific text properties, @code{front-sticky} and @code{rear-nonsticky},
and with the variable @code{text-property-default-nonsticky}.  You can
use the variable to specify a different default for a given property.
You can use those two text properties to make any specific properties
sticky or nonsticky in any particular part of the text.

  If a character's @code{front-sticky} property is @code{t}, then all
its properties are front-sticky.  If the @code{front-sticky} property is
a list, then the sticky properties of the character are those whose
names are in the list.  For example, if a character has a
@code{front-sticky} property whose value is @code{(face read-only)},
then insertion before the character can inherit its @code{face} property
and its @code{read-only} property, but no others.

  The @code{rear-nonsticky} property works the opposite way.  Most
properties are rear-sticky by default, so the @code{rear-nonsticky}
property says which properties are @emph{not} rear-sticky.  If a
character's @code{rear-nonsticky} property is @code{t}, then none of its
properties are rear-sticky.  If the @code{rear-nonsticky} property is a
list, properties are rear-sticky @emph{unless} their names are in the
list.

@defvar text-property-default-nonsticky
This variable holds an alist which defines the default rear-stickiness
of various text properties.  Each element has the form
@code{(@var{property} . @var{nonstickiness})}, and it defines the
stickiness of a particular text property, @var{property}.

If @var{nonstickiness} is non-@code{nil}, this means that the property
@var{property} is rear-nonsticky by default.  Since all properties are
front-nonsticky by default, this makes @var{property} nonsticky in both
directions by default.

The text properties @code{front-sticky} and @code{rear-nonsticky}, when
used, take precedence over the default @var{nonstickiness} specified in
@code{text-property-default-nonsticky}.
@end defvar

  Here are the functions that insert text with inheritance of properties:

@defun insert-and-inherit &rest strings
Insert the strings @var{strings}, just like the function @code{insert},
but inherit any sticky properties from the adjoining text.
@end defun

@defun insert-before-markers-and-inherit &rest strings
Insert the strings @var{strings}, just like the function
@code{insert-before-markers}, but inherit any sticky properties from the
adjoining text.
@end defun

  @xref{Insertion}, for the ordinary insertion functions which do not
inherit.

@node Lazy Properties
@subsection Lazy Computation of Text Properties

  Instead of computing text properties for all the text in the buffer,
you can arrange to compute the text properties for parts of the text
when and if something depends on them.

  The primitive that extracts text from the buffer along with its
properties is @code{buffer-substring}.  Before examining the properties,
this function runs the abnormal hook @code{buffer-access-fontify-functions}.

@defvar buffer-access-fontify-functions
This variable holds a list of functions for computing text properties.
Before @code{buffer-substring} copies the text and text properties for a
portion of the buffer, it calls all the functions in this list.  Each of
the functions receives two arguments that specify the range of the
buffer being accessed.  (The buffer itself is always the current
buffer.)
@end defvar

  The function @code{buffer-substring-no-properties} does not call these
functions, since it ignores text properties anyway.

  In order to prevent the hook functions from being called more than
once for the same part of the buffer, you can use the variable
@code{buffer-access-fontified-property}.

@defvar buffer-access-fontified-property
If this variable's value is non-@code{nil}, it is a symbol which is used
as a text property name.  A non-@code{nil} value for that text property
means the other text properties for this character have already been
computed.

If all the characters in the range specified for @code{buffer-substring}
have a non-@code{nil} value for this property, @code{buffer-substring}
does not call the @code{buffer-access-fontify-functions} functions.  It
assumes these characters already have the right text properties, and
just copies the properties they already have.

The normal way to use this feature is that the
@code{buffer-access-fontify-functions} functions add this property, as
well as others, to the characters they operate on.  That way, they avoid
being called over and over for the same text.
@end defvar

@node Clickable Text
@subsection Defining Clickable Text
@cindex clickable text
@cindex follow links
@cindex mouse-1

  @dfn{Clickable text} is text that can be clicked, with either the
mouse or via a keyboard command, to produce some result.  Many major
modes use clickable text to implement textual hyper-links, or
@dfn{links} for short.

  The easiest way to insert and manipulate links is to use the
@code{button} package.  @xref{Buttons}.  In this section, we will
explain how to manually set up clickable text in a buffer, using text
properties.  For simplicity, we will refer to the clickable text as a
@dfn{link}.

  Implementing a link involves three separate steps: (1) indicating
clickability when the mouse moves over the link; (2) making @key{RET}
or @kbd{mouse-2} on that link do something; and (3) setting up a
@code{follow-link} condition so that the link obeys
@code{mouse-1-click-follows-link}.

  To indicate clickability, add the @code{mouse-face} text property to
the text of the link; then Emacs will highlight the link when the
mouse moves over it.  In addition, you should define a tooltip or echo
area message, using the @code{help-echo} text property.  @xref{Special
Properties}.  For instance, here is how Dired indicates that file
names are clickable:

@smallexample
 (if (dired-move-to-filename)
     (add-text-properties
       (point)
       (save-excursion
         (dired-move-to-end-of-filename)
         (point))
       '(mouse-face highlight
         help-echo "mouse-2: visit this file in other window")))
@end smallexample

  To make the link clickable, bind @key{RET} and @kbd{mouse-2} to
commands that perform the desired action.  Each command should check
to see whether it was called on a link, and act accordingly.  For
instance, Dired's major mode keymap binds @kbd{mouse-2} to the
following command:

@smallexample
(defun dired-mouse-find-file-other-window (event)
  "In Dired, visit the file or directory name you click on."
  (interactive "e")
  (let ((window (posn-window (event-end event)))
        (pos (posn-point (event-end event)))
        file)
    (if (not (windowp window))
        (error "No file chosen"))
    (with-current-buffer (window-buffer window)
      (goto-char pos)
      (setq file (dired-get-file-for-visit)))
    (if (file-directory-p file)
        (or (and (cdr dired-subdir-alist)
                 (dired-goto-subdir file))
            (progn
              (select-window window)
              (dired-other-window file)))
      (select-window window)
      (find-file-other-window (file-name-sans-versions file t)))))
@end smallexample

@noindent
This command uses the functions @code{posn-window} and
@code{posn-point} to determine where the click occurred, and
@code{dired-get-file-for-visit} to determine which file to visit.

  Instead of binding the mouse command in a major mode keymap, you can
bind it within the link text, using the @code{keymap} text property
(@pxref{Special Properties}).  For instance:

@example
(let ((map (make-sparse-keymap)))
  (define-key map [mouse-2] 'operate-this-button)
  (put-text-property link-start link-end 'keymap map))
@end example

@noindent
With this method, you can easily define different commands for
different links.  Furthermore, the global definition of @key{RET} and
@kbd{mouse-2} remain available for the rest of the text in the buffer.

@vindex mouse-1-click-follows-link
  The basic Emacs command for clicking on links is @kbd{mouse-2}.
However, for compatibility with other graphical applications, Emacs
also recognizes @kbd{mouse-1} clicks on links, provided the user
clicks on the link quickly without moving the mouse.  This behavior is
controlled by the user option @code{mouse-1-click-follows-link}.
@xref{Mouse References,,, emacs, The GNU Emacs Manual}.

@kindex follow-link @r{(text or overlay property)}
  To set up the link so that it obeys
@code{mouse-1-click-follows-link}, you must either (1) apply a
@code{follow-link} text or overlay property to the link text, or (2)
bind the @code{follow-link} event to a keymap (which can be a major
mode keymap or a local keymap specified via the @code{keymap} text
property).  The value of the @code{follow-link} property, or the
binding for the @code{follow-link} event, acts as a condition for
the link action.  This condition tells Emacs two things: the
circumstances under which a @kbd{mouse-1} click should be regarded as
occurring inside the link, and how to compute an action code
that says what to translate the @kbd{mouse-1} click into.  The link
action condition can be one of the following:

@table @asis
@item @code{mouse-face}
If the condition is the symbol @code{mouse-face}, a position is inside
a link if there is a non-@code{nil} @code{mouse-face} property at that
position.  The action code is always @code{t}.

For example, here is how Info mode handles @key{mouse-1}:

@smallexample
(define-key Info-mode-map [follow-link] 'mouse-face)
@end smallexample

@item a function
If the condition is a function, @var{func}, then a position @var{pos}
is inside a link if @code{(@var{func} @var{pos})} evaluates to
non-@code{nil}.  The value returned by @var{func} serves as the action
code.

For example, here is how pcvs enables @kbd{mouse-1} to follow links on
file names only:

@smallexample
(define-key map [follow-link]
  (lambda (pos)
    (eq (get-char-property pos 'face) 'cvs-filename-face)))
@end smallexample

@item anything else
If the condition value is anything else, then the position is inside a
link and the condition itself is the action code.  Clearly, you should
specify this kind of condition only when applying the condition via a
text or property overlay on the link text (so that it does not apply
to the entire buffer).
@end table

@noindent
The action code tells @kbd{mouse-1} how to follow the link:

@table @asis
@item a string or vector
If the action code is a string or vector, the @kbd{mouse-1} event is
translated into the first element of the string or vector; i.e., the
action of the @kbd{mouse-1} click is the local or global binding of
that character or symbol.  Thus, if the action code is @code{"foo"},
@kbd{mouse-1} translates into @kbd{f}.  If it is @code{[foo]},
@kbd{mouse-1} translates into @key{foo}.

@item anything else
For any other non-@code{nil} action code, the @kbd{mouse-1} event is
translated into a @kbd{mouse-2} event at the same position.
@end table

  To define @kbd{mouse-1} to activate a button defined with
@code{define-button-type}, give the button a @code{follow-link}
property.  The property value should be a link action condition, as
described above.  @xref{Buttons}.  For example, here is how Help mode
handles @kbd{mouse-1}:

@smallexample
(define-button-type 'help-xref
  'follow-link t
  'action #'help-button-action)
@end smallexample

  To define @kbd{mouse-1} on a widget defined with
@code{define-widget}, give the widget a @code{:follow-link} property.
The property value should be a link action condition, as described
above.  For example, here is how the @code{link} widget specifies that
a @key{mouse-1} click shall be translated to @key{RET}:

@smallexample
(define-widget 'link 'item
  "An embedded link."
  :button-prefix 'widget-link-prefix
  :button-suffix 'widget-link-suffix
  :follow-link "\C-m"
  :help-echo "Follow the link."
  :format "%[%t%]")
@end smallexample

@defun mouse-on-link-p pos
This function returns non-@code{nil} if position @var{pos} in the
current buffer is on a link.  @var{pos} can also be a mouse event
location, as returned by @code{event-start} (@pxref{Accessing Mouse}).
@end defun

@node Fields
@subsection Defining and Using Fields
@cindex fields

  A field is a range of consecutive characters in the buffer that are
identified by having the same value (comparing with @code{eq}) of the
@code{field} property (either a text-property or an overlay property).
This section describes special functions that are available for
operating on fields.

  You specify a field with a buffer position, @var{pos}.  We think of
each field as containing a range of buffer positions, so the position
you specify stands for the field containing that position.

  When the characters before and after @var{pos} are part of the same
field, there is no doubt which field contains @var{pos}: the one those
characters both belong to.  When @var{pos} is at a boundary between
fields, which field it belongs to depends on the stickiness of the
@code{field} properties of the two surrounding characters (@pxref{Sticky
Properties}).  The field whose property would be inherited by text
inserted at @var{pos} is the field that contains @var{pos}.

  There is an anomalous case where newly inserted text at @var{pos}
would not inherit the @code{field} property from either side.  This
happens if the previous character's @code{field} property is not
rear-sticky, and the following character's @code{field} property is not
front-sticky.  In this case, @var{pos} belongs to neither the preceding
field nor the following field; the field functions treat it as belonging
to an empty field whose beginning and end are both at @var{pos}.

  In all of these functions, if @var{pos} is omitted or @code{nil}, the
value of point is used by default.  If narrowing is in effect, then
@var{pos} should fall within the accessible portion.  @xref{Narrowing}.

@defun field-beginning &optional pos escape-from-edge limit
This function returns the beginning of the field specified by @var{pos}.

If @var{pos} is at the beginning of its field, and
@var{escape-from-edge} is non-@code{nil}, then the return value is
always the beginning of the preceding field that @emph{ends} at @var{pos},
regardless of the stickiness of the @code{field} properties around
@var{pos}.

If @var{limit} is non-@code{nil}, it is a buffer position; if the
beginning of the field is before @var{limit}, then @var{limit} will be
returned instead.
@end defun

@defun field-end &optional pos escape-from-edge limit
This function returns the end of the field specified by @var{pos}.

If @var{pos} is at the end of its field, and @var{escape-from-edge} is
non-@code{nil}, then the return value is always the end of the following
field that @emph{begins} at @var{pos}, regardless of the stickiness of
the @code{field} properties around @var{pos}.

If @var{limit} is non-@code{nil}, it is a buffer position; if the end
of the field is after @var{limit}, then @var{limit} will be returned
instead.
@end defun

@defun field-string &optional pos
This function returns the contents of the field specified by @var{pos},
as a string.
@end defun

@defun field-string-no-properties &optional pos
This function returns the contents of the field specified by @var{pos},
as a string, discarding text properties.
@end defun

@defun delete-field &optional pos
This function deletes the text of the field specified by @var{pos}.
@end defun

@defun constrain-to-field new-pos old-pos &optional escape-from-edge only-in-line inhibit-capture-property
This function constrains @var{new-pos} to the field that
@var{old-pos} belongs to---in other words, it returns the position
closest to @var{new-pos} that is in the same field as @var{old-pos}.

If @var{new-pos} is @code{nil}, then @code{constrain-to-field} uses
the value of point instead, and moves point to the resulting position
in addition to returning that position.

If @var{old-pos} is at the boundary of two fields, then the acceptable
final positions depend on the argument @var{escape-from-edge}.  If
@var{escape-from-edge} is @code{nil}, then @var{new-pos} must be in
the field whose @code{field} property equals what new characters
inserted at @var{old-pos} would inherit.  (This depends on the
stickiness of the @code{field} property for the characters before and
after @var{old-pos}.)  If @var{escape-from-edge} is non-@code{nil},
@var{new-pos} can be anywhere in the two adjacent fields.
Additionally, if two fields are separated by another field with the
special value @code{boundary}, then any point within this special
field is also considered to be on the boundary.

Commands like @kbd{C-a} with no argument, that normally move backward
to a specific kind of location and stay there once there, probably
should specify @code{nil} for @var{escape-from-edge}.  Other motion
commands that check fields should probably pass @code{t}.

If the optional argument @var{only-in-line} is non-@code{nil}, and
constraining @var{new-pos} in the usual way would move it to a different
line, @var{new-pos} is returned unconstrained.  This used in commands
that move by line, such as @code{next-line} and
@code{beginning-of-line}, so that they respect field boundaries only in
the case where they can still move to the right line.

If the optional argument @var{inhibit-capture-property} is
non-@code{nil}, and @var{old-pos} has a non-@code{nil} property of that
name, then any field boundaries are ignored.

You can cause @code{constrain-to-field} to ignore all field boundaries
(and so never constrain anything) by binding the variable
@code{inhibit-field-text-motion} to a non-@code{nil} value.
@end defun

@node Not Intervals
@subsection Why Text Properties are not Intervals
@cindex intervals

  Some editors that support adding attributes to text in the buffer do
so by letting the user specify intervals within the text, and adding
the properties to the intervals.  Those editors permit the user or the
programmer to determine where individual intervals start and end.  We
deliberately provided a different sort of interface in Emacs Lisp to
avoid certain paradoxical behavior associated with text modification.

  If the actual subdivision into intervals is meaningful, that means you
can distinguish between a buffer that is just one interval with a
certain property, and a buffer containing the same text subdivided into
two intervals, both of which have that property.

  Suppose you take the buffer with just one interval and kill part of
the text.  The text remaining in the buffer is one interval, and the
copy in the kill ring (and the undo list) becomes a separate interval.
Then if you yank back the killed text, you get two intervals with the
same properties.  Thus, editing does not preserve the distinction
between one interval and two.

  Suppose we attempt to fix this problem by coalescing the two intervals when
the text is inserted.  That works fine if the buffer originally was a
single interval.  But suppose instead that we have two adjacent
intervals with the same properties, and we kill the text of one interval
and yank it back.  The same interval-coalescence feature that rescues
the other case causes trouble in this one: after yanking, we have just
one interval.  Once again, editing does not preserve the distinction
between one interval and two.

  Insertion of text at the border between intervals also raises
questions that have no satisfactory answer.

  However, it is easy to arrange for editing to behave consistently
for questions of the form, ``What are the properties of text at this
buffer or string position?''  So we have decided these are the only
questions that make sense; we have not implemented asking questions
about where intervals start or end.

  In practice, you can usually use the text property search functions in
place of explicit interval boundaries.  You can think of them as finding
the boundaries of intervals, assuming that intervals are always
coalesced whenever possible.  @xref{Property Search}.

  Emacs also provides explicit intervals as a presentation feature; see
@ref{Overlays}.

@node Substitution
@section Substituting for a Character Code
@cindex replace characters in region
@cindex substitute characters

  The following functions replace characters within a specified region
based on their character codes.

@defun subst-char-in-region start end old-char new-char &optional noundo
@cindex replace characters
This function replaces all occurrences of the character @var{old-char}
with the character @var{new-char} in the region of the current buffer
defined by @var{start} and @var{end}.

@cindex undo avoidance
If @var{noundo} is non-@code{nil}, then @code{subst-char-in-region} does
not record the change for undo and does not mark the buffer as modified.
This was useful for controlling the old selective display feature
(@pxref{Selective Display}).

@code{subst-char-in-region} does not move point and returns
@code{nil}.

@example
@group
---------- Buffer: foo ----------
This is the contents of the buffer before.
---------- Buffer: foo ----------
@end group

@group
(subst-char-in-region 1 20 ?i ?X)
     @result{} nil

---------- Buffer: foo ----------
ThXs Xs the contents of the buffer before.
---------- Buffer: foo ----------
@end group
@end example
@end defun

@deffn Command translate-region start end table
This function applies a translation table to the characters in the
buffer between positions @var{start} and @var{end}.

The translation table @var{table} is a string or a char-table;
@code{(aref @var{table} @var{ochar})} gives the translated character
corresponding to @var{ochar}.  If @var{table} is a string, any
characters with codes larger than the length of @var{table} are not
altered by the translation.

The return value of @code{translate-region} is the number of
characters that were actually changed by the translation.  This does
not count characters that were mapped into themselves in the
translation table.
@end deffn

@node Registers
@section Registers
@cindex registers

  A register is a sort of variable used in Emacs editing that can hold a
variety of different kinds of values.  Each register is named by a
single character.  All @acronym{ASCII} characters and their meta variants
(but with the exception of @kbd{C-g}) can be used to name registers.
Thus, there are 255 possible registers.  A register is designated in
Emacs Lisp by the character that is its name.

@defvar register-alist
This variable is an alist of elements of the form @code{(@var{name} .
@var{contents})}.  Normally, there is one element for each Emacs
register that has been used.

The object @var{name} is a character (an integer) identifying the
register.
@end defvar

  The @var{contents} of a register can have several possible types:

@table @asis
@item a number
A number stands for itself.  If @code{insert-register} finds a number
in the register, it converts the number to decimal.

@item a marker
A marker represents a buffer position to jump to.

@item a string
A string is text saved in the register.

@item a rectangle
@cindex rectangle, as contents of a register
A rectangle is represented by a list of strings.

@item @code{(@var{window-configuration} @var{position})}
This represents a window configuration to restore in one frame, and a
position to jump to in the current buffer.

@c FIXME: Mention frameset here.
@item @code{(@var{frame-configuration} @var{position})}
This represents a frame configuration to restore, and a position
to jump to in the current buffer.

@item (file @var{filename})
This represents a file to visit; jumping to this value visits file
@var{filename}.

@item (file-query @var{filename} @var{position})
This represents a file to visit and a position in it; jumping to this
value visits file @var{filename} and goes to buffer position
@var{position}.  Restoring this type of position asks the user for
confirmation first.
@end table

  The functions in this section return unpredictable values unless
otherwise stated.

@defun get-register reg
This function returns the contents of the register
@var{reg}, or @code{nil} if it has no contents.
@end defun

@defun set-register reg value
This function sets the contents of register @var{reg} to @var{value}.
A register can be set to any value, but the other register functions
expect only certain data types.  The return value is @var{value}.
@end defun

@deffn Command view-register reg
This command displays what is contained in register @var{reg}.
@end deffn

@deffn Command insert-register reg &optional beforep
This command inserts contents of register @var{reg} into the current
buffer.

Normally, this command puts point before the inserted text, and the
mark after it.  However, if the optional second argument @var{beforep}
is non-@code{nil}, it puts the mark before and point after.

When called interactively, the command defaults to putting point after
text, and a prefix argument inverts this behavior.

If the register contains a rectangle, then the rectangle is inserted
with its upper left corner at point.  This means that text is inserted
in the current line and underneath it on successive lines.

If the register contains something other than saved text (a string) or
a rectangle (a list), currently useless things happen.  This may be
changed in the future.
@end deffn

@defun register-read-with-preview prompt
@cindex register preview
This function reads and returns a register name, prompting with
@var{prompt} and possibly showing a preview of the existing registers
and their contents.  The preview is shown in a temporary window, after
the delay specified by the user option @code{register-preview-delay},
if its value and @code{register-alist} are both non-@code{nil}.  The
preview is also shown if the user requests help (e.g., by typing the
help character).  We recommend that all interactive commands which
read register names use this function.
@end defun

@node Transposition
@section Transposition of Text

  This function can be used to transpose stretches of text:

@defun transpose-regions start1 end1 start2 end2 &optional leave-markers
This function exchanges two nonoverlapping portions of the buffer (if
they overlap, the function signals an error).  Arguments @var{start1}
and @var{end1} specify the bounds of one portion and arguments
@var{start2} and @var{end2} specify the bounds of the other portion.

Normally, @code{transpose-regions} relocates markers with the transposed
text; a marker previously positioned within one of the two transposed
portions moves along with that portion, thus remaining between the same
two characters in their new position.  However, if @var{leave-markers}
is non-@code{nil}, @code{transpose-regions} does not do this---it leaves
all markers unrelocated.
@end defun

@node Replacing
@section Replacing Buffer Text

  You can use the following function to replace the text of one buffer
with the text of another buffer:

@deffn Command replace-buffer-contents source &optional max-secs max-costs
This function replaces the accessible portion of the current buffer
with the accessible portion of the buffer @var{source}.  @var{source}
may either be a buffer object or the name of a buffer.  When
@code{replace-buffer-contents} succeeds, the text of the accessible
portion of the current buffer will be equal to the text of the
accessible portion of the @var{source} buffer.

This function attempts to keep point, markers, text properties, and
overlays in the current buffer intact.  One potential case where this
behavior is useful is external code formatting programs: they
typically write the reformatted text into a temporary buffer or file,
and using @code{delete-region} and @code{insert-buffer-substring}
would destroy these properties.  However, the latter combination is
typically faster (@xref{Deletion}, and @ref{Insertion}).

For its working, @code{replace-buffer-contents} needs to compare the
contents of the original buffer with that of @code{source} which is a
costly operation if the buffers are huge and there is a high number of
differences between them.  In order to keep
@code{replace-buffer-contents}'s runtime in bounds, it has two
optional arguments.

@code{max-secs} defines a hard boundary in terms of seconds.  If given
and exceeded, it will fall back to @code{delete-region} and
@code{insert-buffer-substring}.

@code{max-costs} defines the quality of the difference computation.
If the actual costs exceed this limit, heuristics are used to provide
a faster but suboptimal solution.  The default value is 1000000.

@code{replace-buffer-contents} returns t if a non-destructive
replacement could be performed.  Otherwise, i.e., if @code{max-secs}
was exceeded, it returns nil.
@end deffn

@defun replace-region-contents beg end replace-fn &optional max-secs max-costs
This function replaces the region between @code{beg} and @code{end}
using the given @code{replace-fn}.  The function @code{replace-fn} is
run in the current buffer narrowed to the specified region and it
should return either a string or a buffer replacing the region.

The replacement is performed using @code{replace-buffer-contents} (see
above) which also describes the @code{max-secs} and @code{max-costs}
arguments and the return value.

Note: If the replacement is a string, it will be placed in a temporary
buffer so that @code{replace-buffer-contents} can operate on it.
Therefore, if you already have the replacement in a buffer, it makes
no sense to convert it to a string using @code{buffer-substring} or
similar.
@end defun

@node Decompression
@section Dealing With Compressed Data

When @code{auto-compression-mode} is enabled, Emacs automatically
uncompresses compressed files when you visit them, and automatically
recompresses them if you alter and save them.  @xref{Compressed
Files,,, emacs, The GNU Emacs Manual}.

The above feature works by calling an external executable (e.g.,
@command{gzip}).  Emacs can also be compiled with support for built-in
decompression using the zlib library, which is faster than calling an
external program.

@defun zlib-available-p
This function returns non-@code{nil} if built-in zlib decompression is
available.
@end defun

@defun zlib-decompress-region start end &optional allow-partial
This function decompresses the region between @var{start} and
@var{end}, using built-in zlib decompression.  The region should
contain data that were compressed with gzip or zlib.  On success, the
function replaces the contents of the region with the decompressed
data.  If @var{allow-partial} is @code{nil} or omitted, then on
failure, the function leaves the region unchanged and returns
@code{nil}.  Otherwise, it returns the number of bytes that were not
decompressed and replaces the region text by whatever data was
successfully decompressed.  This function can be called only in
unibyte buffers.
@end defun


@node Base 64
@section Base 64 Encoding
@cindex base 64 encoding

  Base 64 code is used in email to encode a sequence of 8-bit bytes as
a longer sequence of @acronym{ASCII} graphic characters.  It is defined in
Internet RFC@footnote{
An RFC, an acronym for @dfn{Request for Comments}, is a numbered
Internet informational document describing a standard.  RFCs are
usually written by technical experts acting on their own initiative,
and are traditionally written in a pragmatic, experience-driven
manner.
}2045 and also in RFC 4648.  This section describes the functions for
converting to and from this code.

@deffn Command base64-encode-region beg end &optional no-line-break
This function converts the region from @var{beg} to @var{end} into base
64 code.  It returns the length of the encoded text.  An error is
signaled if a character in the region is multibyte, i.e., in a
multibyte buffer the region must contain only characters from the
charsets @code{ascii}, @code{eight-bit-control} and
@code{eight-bit-graphic}.

Normally, this function inserts newline characters into the encoded
text, to avoid overlong lines.  However, if the optional argument
@var{no-line-break} is non-@code{nil}, these newlines are not added, so
the output is just one long line.
@end deffn

@deffn Command base64url-encode-region beg end &optional no-pad
This function is like @code{base64-encode-region}, but it implements
the URL variant of base 64 encoding, per RFC 4648, and it doesn't
insert newline characters into the encoded text, so the output is
just one long line.

If the optional argument @var{no-pad} is non-@code{nil} then this
function doesn't generate the padding (@code{=}).
@end deffn

@defun base64-encode-string string &optional no-line-break
This function converts the string @var{string} into base 64 code.  It
returns a string containing the encoded text.  As for
@code{base64-encode-region}, an error is signaled if a character in the
string is multibyte.

Normally, this function inserts newline characters into the encoded
text, to avoid overlong lines.  However, if the optional argument
@var{no-line-break} is non-@code{nil}, these newlines are not added, so
the result string is just one long line.
@end defun

@defun base64url-encode-string string &optional no-pad
Like @code{base64-encode-string}, but generates the URL variant of
base 64, and doesn't insert newline characters into the encoded text,
so the result is just one long line.

If the optional argument @var{no-pad} is non-@code{nil} then this
function doesn't generate the padding.
@end defun

@deffn Command base64-decode-region beg end &optional base64url
This function converts the region from @var{beg} to @var{end} from base
64 code into the corresponding decoded text.  It returns the length of
the decoded text.

The decoding functions ignore newline characters in the encoded text.

If optional argument @var{base64url} is is non-@code{nil}, then padding
is optional, and the URL variant of base 64 encoding is used.
@end deffn

@defun base64-decode-string string &optional base64url
This function converts the string @var{string} from base 64 code into
the corresponding decoded text.  It returns a unibyte string containing the
decoded text.

The decoding functions ignore newline characters in the encoded text.


If optional argument @var{base64url} is is non-@code{nil}, then padding
is optional, and the URL variant of base 64 encoding is used.
@end defun

@node Checksum/Hash
@section Checksum/Hash
@cindex MD5 checksum
@cindex SHA hash
@cindex hash, cryptographic
@cindex cryptographic hash

  Emacs has built-in support for computing @dfn{cryptographic hashes}.
A cryptographic hash, or @dfn{checksum}, is a digital fingerprint
of a piece of data (e.g., a block of text) which can be used to check
that you have an unaltered copy of that data.

@cindex message digest
  Emacs supports several common cryptographic hash algorithms: MD5,
SHA-1, SHA-2, SHA-224, SHA-256, SHA-384 and SHA-512.  MD5 is the
oldest of these algorithms, and is commonly used in @dfn{message
digests} to check the integrity of messages transmitted over a
network.  MD5 is not collision resistant (i.e., it is possible to
deliberately design different pieces of data which have the same MD5
hash), so you should not used it for anything security-related.  A
similar theoretical weakness also exists in SHA-1.  Therefore, for
security-related applications you should use the other hash types,
such as SHA-2.

@defun secure-hash-algorithms
This function returns a list of symbols representing algorithms that
@code{secure-hash} can use.
@end defun

@defun secure-hash algorithm object &optional start end binary
This function returns a hash for @var{object}.  The argument
@var{algorithm} is a symbol stating which hash to compute: one of
@code{md5}, @code{sha1}, @code{sha224}, @code{sha256}, @code{sha384}
or @code{sha512}.  The argument @var{object} should be a buffer or a
string.

The optional arguments @var{start} and @var{end} are character
positions specifying the portion of @var{object} to compute the
message digest for.  If they are @code{nil} or omitted, the hash is
computed for the whole of @var{object}.

If the argument @var{binary} is omitted or @code{nil}, the function
returns the @dfn{text form} of the hash, as an ordinary Lisp string.
If @var{binary} is non-@code{nil}, it returns the hash in @dfn{binary
form}, as a sequence of bytes stored in a unibyte string.

This function does not compute the hash directly from the internal
representation of @var{object}'s text (@pxref{Text Representations}).
Instead, it encodes the text using a coding system (@pxref{Coding
Systems}), and computes the hash from that encoded text.  If
@var{object} is a buffer, the coding system used is the one which
would be chosen by default for writing the text into a file.  If
@var{object} is a string, the user's preferred coding system is used
(@pxref{Recognize Coding,,, emacs, GNU Emacs Manual}).
@end defun

@defun md5 object &optional start end coding-system noerror
This function returns an MD5 hash.  It is semi-obsolete, since for
most purposes it is equivalent to calling @code{secure-hash} with
@code{md5} as the @var{algorithm} argument.  The @var{object},
@var{start} and @var{end} arguments have the same meanings as in
@code{secure-hash}.

If @var{coding-system} is non-@code{nil}, it specifies a coding system
to use to encode the text; if omitted or @code{nil}, the default
coding system is used, like in @code{secure-hash}.

Normally, @code{md5} signals an error if the text can't be encoded
using the specified or chosen coding system.  However, if
@var{noerror} is non-@code{nil}, it silently uses @code{raw-text}
coding instead.
@end defun

@defun buffer-hash &optional buffer-or-name
Return a hash of @var{buffer-or-name}.  If @code{nil}, this defaults
to the current buffer.  As opposed to @code{secure-hash}, this
function computes the hash based on the internal representation of the
buffer, disregarding any coding systems.  It's therefore only useful
when comparing two buffers running in the same Emacs, and is not
guaranteed to return the same hash between different Emacs versions.
It should be somewhat more efficient on larger buffers than
@code{secure-hash} is, and should not allocate more memory.
@c Note that we do not document what hashing function we're using, or
@c even whether it's a cryptographic hash, since that may change
@c according to what we find useful.
@end defun

@node GnuTLS Cryptography
@section GnuTLS Cryptography
@cindex MD5 checksum
@cindex SHA hash
@cindex hash, cryptographic
@cindex cryptographic hash
@cindex AEAD cipher
@cindex cipher, AEAD
@cindex symmetric cipher
@cindex cipher, symmetric

  If compiled with GnuTLS, Emacs offers built-in cryptographic
support.  Following the GnuTLS API terminology, the available tools
are digests, MACs, symmetric ciphers, and AEAD ciphers.

The terms used herein, such as IV (Initialization Vector), require
some familiarity with cryptography and will not be defined in detail.
Please consult @uref{https://www.gnutls.org/} for specific
documentation which may help you understand the terminology and
structure of the GnuTLS library.

@menu
* Format of GnuTLS Cryptography Inputs::
* GnuTLS Cryptographic Functions::
@end menu

@node Format of GnuTLS Cryptography Inputs
@subsection Format of GnuTLS Cryptography Inputs
@cindex format of gnutls cryptography inputs
@cindex gnutls cryptography inputs format

  The inputs to GnuTLS cryptographic functions can be specified in
several ways, both as primitive Emacs Lisp types or as lists.

The list form is currently similar to how @code{md5} and
@code{secure-hash} operate.

@table @code
@item @var{buffer}
Simply passing a buffer as input means the whole buffer should be used.

@item @var{string}
A string as input will be used directly.  It may be modified by the
function (unlike most other Emacs Lisp functions) to reduce the chance
of exposing sensitive data after the function does its work.

@item (@var{buffer-or-string} @var{start} @var{end} @var{coding-system} @var{noerror})
This specifies a buffer or a string as described above, but an
optional range can be specified with @var{start} and @var{end}.

In addition an optional @var{coding-system} can be specified if needed.

The last optional item, @var{noerror}, overrides the normal error when
the text can't be encoded using the specified or chosen coding system.
When @var{noerror} is non-@code{nil}, this function silently uses
@code{raw-text} coding instead.

@item (@code{iv-auto} @var{length})
This will generate an IV (Initialization Vector) of the specified
length using the GnuTLS @code{GNUTLS_RND_NONCE} generator and pass it
to the function.  This ensures that the IV is unpredictable and
unlikely to be reused in the same session.  The actual value of the IV
is returned by the function as described below.

@end table

@node GnuTLS Cryptographic Functions
@subsection GnuTLS Cryptographic Functions
@cindex gnutls cryptographic functions

@defun gnutls-digests
This function returns the alist of the GnuTLS digest algorithms.

Each entry has a key which represents the algorithm, followed by a
plist with internal details about the algorithm.  The plist will have
@code{:type gnutls-digest-algorithm} and also will have the key
@code{:digest-algorithm-length 64} to indicate the size, in bytes, of
the resulting digest.

There is a name parallel between GnuTLS MAC and digest algorithms but
they are separate things internally and should not be mixed.
@end defun

@defun gnutls-hash-digest digest-method input
The @var{digest-method} can be the whole plist from
@code{gnutls-digests}, or just the symbol key, or a string with the
name of that symbol.

The @var{input} can be specified as a buffer or string or in other
ways (@pxref{Format of GnuTLS Cryptography Inputs}).

This function returns @code{nil} on error, and signals a Lisp error if
the @var{digest-method} or @var{input} are invalid.  On success, it
returns a list of a binary string (the output) and the IV used.
@end defun

@defun gnutls-macs
This function returns the alist of the GnuTLS MAC algorithms.

Each entry has a key which represents the algorithm, followed by a
plist with internal details about the algorithm.  The plist will have
@code{:type gnutls-mac-algorithm} and also will have the keys
@code{:mac-algorithm-length} @code{:mac-algorithm-keysize}
@code{:mac-algorithm-noncesize} to indicate the size, in bytes, of the
resulting hash, the key, and the nonce respectively.

The nonce is currently unused and only some MACs support it.

There is a name parallel between GnuTLS MAC and digest algorithms but
they are separate things internally and should not be mixed.
@end defun

@defun gnutls-hash-mac hash-method key input
The @var{hash-method} can be the whole plist from
@code{gnutls-macs}, or just the symbol key, or a string with the
name of that symbol.

The @var{key} can be specified as a buffer or string or in other ways
(@pxref{Format of GnuTLS Cryptography Inputs}).  The @var{key} will be
wiped after use if it's a string.

The @var{input} can be specified as a buffer or string or in other
ways (@pxref{Format of GnuTLS Cryptography Inputs}).

This function returns @code{nil} on error, and signals a Lisp error if
the @var{hash-method} or @var{key} or @var{input} are invalid.

On success, it returns a list of a binary string (the output) and the
IV used.
@end defun

@defun gnutls-ciphers
This function returns the alist of the GnuTLS ciphers.

Each entry has a key which represents the cipher, followed by a plist
with internal details about the algorithm.  The plist will have
@code{:type gnutls-symmetric-cipher} and also will have the keys
@code{:cipher-aead-capable} set to @code{nil} or @code{t} to indicate
AEAD capability; and @code{:cipher-tagsize} @code{:cipher-blocksize}
@code{:cipher-keysize} @code{:cipher-ivsize} to indicate the size, in
bytes, of the tag, block size of the resulting data, the key, and the
IV respectively.
@end defun

@defun gnutls-symmetric-encrypt cipher key iv input &optional aead_auth
The @var{cipher} can be the whole plist from
@code{gnutls-ciphers}, or just the symbol key, or a string with the
name of that symbol.

The @var{key} can be specified as a buffer or string or in other ways
(@pxref{Format of GnuTLS Cryptography Inputs}).  The @var{key} will be
wiped after use if it's a string.

The @var{iv} and @var{input} and the optional @var{aead_auth} can be
specified as a buffer or string or in other ways (@pxref{Format of
GnuTLS Cryptography Inputs}).

@var{aead_auth} is only checked with AEAD ciphers, that is, ciphers whose
plist has @code{:cipher-aead-capable t}.  Otherwise it's ignored.

This function returns @code{nil} on error, and signals a Lisp error if
the @var{cipher} or @var{key}, @var{iv}, or @var{input} are invalid,
or if @var{aead_auth} was specified with an AEAD cipher and was
invalid.

On success, it returns a list of a binary string (the output) and the
IV used.
@end defun

@defun gnutls-symmetric-decrypt cipher key iv input &optional aead_auth
The @var{cipher} can be the whole plist from
@code{gnutls-ciphers}, or just the symbol key, or a string with the
name of that symbol.

The @var{key} can be specified as a buffer or string or in other ways
(@pxref{Format of GnuTLS Cryptography Inputs}).  The @var{key} will be
wiped after use if it's a string.

The @var{iv} and @var{input} and the optional @var{aead_auth} can be
specified as a buffer or string or in other ways (@pxref{Format of
GnuTLS Cryptography Inputs}).

@var{aead_auth} is only checked with AEAD ciphers, that is, ciphers whose
plist has @code{:cipher-aead-capable t}.  Otherwise it's ignored.

This function returns @code{nil} on decryption error, and signals a
Lisp error if the @var{cipher} or @var{key}, @var{iv}, or @var{input}
are invalid, or if @var{aead_auth} was specified with an AEAD cipher
and was invalid.

On success, it returns a list of a binary string (the output) and the
IV used.
@end defun

@node Parsing HTML/XML
@section Parsing HTML and XML
@cindex parsing html

  Emacs can be compiled with built-in libxml2 support.

@defun libxml-available-p
This function returns non-@code{nil} if built-in libxml2 support is
available in this Emacs session.
@end defun

When libxml2 support is available, the following functions can be used
to parse HTML or XML text into Lisp object trees.

@defun libxml-parse-html-region start end &optional base-url discard-comments
This function parses the text between @var{start} and @var{end} as
HTML, and returns a list representing the HTML @dfn{parse tree}.  It
attempts to handle real-world HTML by robustly coping with syntax
mistakes.

The optional argument @var{base-url}, if non-@code{nil}, should be a
string specifying the base URL for relative URLs occurring in links.

If the optional argument @var{discard-comments} is non-@code{nil},
any top-level comment is discarded.  (This argument is obsolete and
will be removed in future Emacs versions.  To remove comments, use the
@code{xml-remove-comments} utility function on the data before you
call the parsing function.)

In the parse tree, each HTML node is represented by a list in which
the first element is a symbol representing the node name, the second
element is an alist of node attributes, and the remaining elements are
the subnodes.

The following example demonstrates this.  Given this (malformed) HTML
document:

@example
<html><head></head><body width=101><div class=thing>Foo<div>Yes
@end example

@noindent
A call to @code{libxml-parse-html-region} returns this @acronym{DOM}
(document object model):

@example
(html nil
 (head nil)
 (body ((width . "101"))
  (div ((class . "thing"))
   "Foo"
   (div nil
    "Yes"))))
@end example
@end defun

@cindex rendering html
@defun shr-insert-document dom
This function renders the parsed HTML in @var{dom} into the current
buffer.  The argument @var{dom} should be a list as generated by
@code{libxml-parse-html-region}.  This function is, e.g., used by
@ref{Top, EWW,, eww, The Emacs Web Wowser Manual}.
@end defun

@cindex parsing xml
@defun libxml-parse-xml-region start end &optional base-url discard-comments
This function is the same as @code{libxml-parse-html-region}, except
that it parses the text as XML rather than HTML (so it is stricter
about syntax).
@end defun

@menu
* Document Object Model:: Access, manipulate and search the @acronym{DOM}.
@end menu

@node Document Object Model
@subsection Document Object Model
@cindex HTML DOM
@cindex XML DOM
@cindex DOM
@cindex Document Object Model

  The @acronym{DOM} returned by @code{libxml-parse-html-region} (and
the other @acronym{XML} parsing functions) is a tree structure where
each node has a node name (called a @dfn{tag}), and optional key/value
@dfn{attribute} list, and then a list of @dfn{child nodes}.  The child
nodes are either strings or @acronym{DOM} objects.

@example
(body ((width . "101"))
 (div ((class . "thing"))
  "Foo"
  (div nil
   "Yes")))
@end example

@defun dom-node tag &optional attributes &rest children
This function creates a @acronym{DOM} node of type @var{tag}.  If
given, @var{attributes} should be a key/value pair list.
If given, @var{children} should be @acronym{DOM} nodes.
@end defun

The following functions can be used to work with this structure.  Each
function takes a @acronym{DOM} node, or a list of nodes.  In the
latter case, only the first node in the list is used.

Simple accessors:

@table @code
@item dom-tag @var{node}
Return the @dfn{tag} (also called ``node name'') of the node.

@item dom-attr @var{node} @var{attribute}
Return the value of @var{attribute} in the node.  A common usage
would be:

@lisp
(dom-attr img 'href)
=> "https://fsf.org/logo.png"
@end lisp

@item dom-children @var{node}
Return all the children of the node.

@item dom-non-text-children @var{node}
Return all the non-string children of the node.

@item dom-attributes @var{node}
Return the key/value pair list of attributes of the node.

@item dom-text @var{node}
Return all the textual elements of the node as a concatenated string.

@item dom-texts @var{node}
Return all the textual elements of the node, as well as the textual
elements of all the children of the node, recursively, as a
concatenated string.  This function also takes an optional separator
to be inserted between the textual elements.

@item dom-parent @var{dom} @var{node}
Return the parent of @var{node} in @var{dom}.

@item dom-remove @var{dom} @var{node}
Remove @var{node} from @var{dom}.
@end table

The following are functions for altering the @acronym{DOM}.

@table @code
@item dom-set-attribute @var{node} @var{attribute} @var{value}
Set the @var{attribute} of the node to @var{value}.

@item dom-append-child @var{node} @var{child}
Append @var{child} as the last child of @var{node}.

@item dom-add-child-before @var{node} @var{child} @var{before}
Add @var{child} to @var{node}'s child list before the @var{before}
node.  If @var{before} is @code{nil}, make @var{child} the first child.

@item dom-set-attributes @var{node} @var{attributes}
Replace all the attributes of the node with a new key/value list.
@end table

The following are functions for searching for elements in the
@acronym{DOM}.  They all return lists of matching nodes.

@table @code
@item dom-by-tag @var{dom} @var{tag}
Return all nodes in @var{dom} that are of type @var{tag}.  A typical
use would be:

@lisp
(dom-by-tag dom 'td)
=> '((td ...) (td ...) (td ...))
@end lisp

@item dom-by-class @var{dom} @var{match}
Return all nodes in @var{dom} that have class names that match
@var{match}, which is a regular expression.

@item dom-by-style @var{dom} @var{style}
Return all nodes in @var{dom} that have styles that match @var{match},
which is a regular expression.

@item dom-by-id @var{dom} @var{style}
Return all nodes in @var{dom} that have IDs that match @var{match},
which is a regular expression.

@item dom-strings @var{dom}
Return all strings in @var{dom}.

@end table

Utility functions:

@table @code
@item dom-pp @var{dom} &optional @var{remove-empty}
Pretty-print @var{dom} at point.  If @var{remove-empty}, don't print
textual nodes that just contain white-space.
@end table


@node Parsing JSON
@section Parsing and generating JSON values
@cindex JSON
@cindex JavaScript Object Notation

  When Emacs is compiled with @acronym{JSON} (@dfn{JavaScript Object
Notation}) support, it provides several functions to convert
between Lisp objects and JSON values.  Any JSON value can be converted
to a Lisp object, but not vice versa.  Specifically:

@itemize
@item
JSON uses three keywords: @code{true}, @code{null}, @code{false}.
@code{true} is represented by the symbol @code{t}.  By default, the
remaining two are represented, respectively, by the symbols
@code{:null} and @code{:false}.

@item
JSON only has floating-point numbers.  They can represent both Lisp
integers and Lisp floating-point numbers.

@item
JSON strings are always Unicode strings encoded in UTF-8.  Lisp
strings can contain non-Unicode characters.

@item
JSON has only one sequence type, the array.  JSON arrays are
represented using Lisp vectors.

@item
JSON has only one map type, the object.  JSON objects are represented
using Lisp hashtables, alists or plists.  When an alist or plist
contains several elements with the same key, Emacs uses only the first
element for serialization, in accordance with the behavior of
@code{assq}.
@end itemize

@noindent
Note that @code{nil}, being both a valid alist and a valid plist,
represents @code{@{@}}, the empty JSON object; not @code{null},
@code{false}, or an empty array, all of which are different JSON
values.

  If some Lisp object can't be represented in JSON, the serialization
functions will signal an error of type @code{wrong-type-argument}.
The parsing functions can also signal the following errors:

@table @code
@item json-end-of-file
Signaled when encountering a premature end of the input text.

@item json-trailing-content
Signaled when encountering unexpected input after the first JSON
object parsed.

@item json-parse-error
Signaled when encountering invalid JSON syntax.
@end table

  Only top-level values (arrays and objects) can be serialized to
JSON.  The subobjects within these top-level values can be of any
type.  Likewise, the parsing functions will only return vectors,
hashtables, alists, and plists.

@defun json-serialize object &rest args
This function returns a new Lisp string which contains the JSON
representation of @var{object}.  The argument @var{args} is a list of
keyword/argument pairs.  The following keywords are accepted:

@table @code
@item :null-object
The value decides which Lisp object to use to represent the JSON
keyword @code{null}.  It defaults to the symbol @code{:null}.

@item :false-object
The value decides which Lisp object to use to represent the JSON
keyword @code{false}.  It defaults to the symbol @code{:false}.
@end table

@end defun

@defun json-insert object &rest args
This function inserts the JSON representation of @var{object} into the
current buffer before point.  The argument @var{args} are interpreted
as in @code{json-parse-string}.
@end defun

@defun json-parse-string string &rest args
This function parses the JSON value in @var{string}, which must be a
Lisp string.  If @var{string} doesn't contain a valid JSON object,
this function signals the @code{json-parse-error} error.

The argument @var{args} is a list of keyword/argument pairs.  The
following keywords are accepted:

@table @code
@item :object-type
The value decides which Lisp object to use for representing the
key-value mappings of a JSON object.  It can be either
@code{hash-table}, the default, to make hashtables with strings as
keys; @code{alist} to use alists with symbols as keys; or @code{plist}
to use plists with keyword symbols as keys.

@item :array-type
The value decides which Lisp object to use for representing a JSON
array.  It can be either @code{array}, the default, to use Lisp
arrays; or @code{list} to use lists.

@item :null-object
The value decides which Lisp object to use to represent the JSON
keyword @code{null}.  It defaults to the symbol @code{:null}.

@item :false-object
The value decides which Lisp object to use to represent the JSON
keyword @code{false}.  It defaults to the symbol @code{:false}.
@end table

@end defun

@defun json-parse-buffer &rest args
This function reads the next JSON value from the current buffer,
starting at point.  It moves point to the position immediately after
the value if contains a valid JSON object; otherwise it signals the
@code{json-parse-error} error and doesn't move point.  The arguments
@var{args} are interpreted as in @code{json-parse-string}.
@end defun

@node JSONRPC
@section JSONRPC communication
@cindex JSON remote procedure call protocol
@cindex JSONRPC

The @code{jsonrpc} library implements the @acronym{JSONRPC}
specification, version 2.0, as it is described in
@uref{http://www.jsonrpc.org/}.  As the name suggests, JSONRPC is a
generic @dfn{Remote Procedure Call} protocol designed around
@acronym{JSON} objects, which you can convert to and from Lisp objects
(@pxref{Parsing JSON}).

@menu
* JSONRPC Overview::
* Process-based JSONRPC connections::
* JSONRPC JSON object format::
* JSONRPC deferred requests::
@end menu

@node JSONRPC Overview
@subsection Overview

Quoting from the @uref{http://www.jsonrpc.org/, spec}, JSONRPC "is
transport agnostic in that the concepts can be used within the same
process, over sockets, over http, or in many various message passing
environments."

@findex jsonrpc-connection
To model this agnosticism, the @code{jsonrpc} library uses objects of
a @code{jsonrpc-connection} class, which represent a connection to a
remote JSON endpoint (for details on Emacs's object system,
@pxref{Top,EIEIO,,eieio,EIEIO}).  In modern object-oriented parlance,
this class is ``abstract'', i.e.@: the actual class of a useful
connection object is always a subclass of @code{jsonrpc-connection}.
Nevertheless, we can define two distinct APIs around the
@code{jsonrpc-connection} class:

@cindex JSONRPC application interfaces
@enumerate

@item A user interface for building JSONRPC applications

@findex :request-dispatcher
@findex :notification-dispatcher
@findex jsonrpc-notify
@findex jsonrpc-request
@findex jsonrpc-async-request
In this scenario, the JSONRPC application selects a concrete subclass
of @code{jsonrpc-connection}, and proceeds to create objects of that
subclass using @code{make-instance}.  To initiate a contact to the
remote endpoint, the JSONRPC application passes this object to the
functions @code{jsonrpc-notify}, @code{jsonrpc-request}, and/or
@code{jsonrpc-async-request}.  For handling remotely initiated
contacts, which generally come in asynchronously, the instantiation
should include @code{:request-dispatcher} and
@code{:notification-dispatcher} initargs, which are both functions of
3 arguments: the connection object; a symbol naming the JSONRPC method
invoked remotely; and a JSONRPC @code{params} object.

@findex jsonrpc-error
The function passed as @code{:request-dispatcher} is responsible for
handling the remote endpoint's requests, which expect a reply from the
local endpoint (in this case, the program you're building).  Inside
that function, you may either return locally (a normal return) or
non-locally (an error return).  A local return value must be a Lisp
object that can be serialized as JSON (@pxref{Parsing JSON}).  This
determines a success response, and the object is forwarded to the
server as the JSONRPC @code{result} object.  A non-local return,
achieved by calling the function @code{jsonrpc-error}, causes an error
response to be sent to the server.  The details of the accompanying
JSONRPC @code{error} are filled out with whatever was passed to
@code{jsonrpc-error}.  A non-local return triggered by an unexpected
error of any other type also causes an error response to be sent
(unless you have set @code{debug-on-error}, in which case this calls
the Lisp debugger, @pxref{Error Debugging}).

@item A inheritance interface for building JSONRPC transport implementations

In this scenario, @code{jsonrpc-connection} is subclassed to implement
a different underlying transport strategy (for details on how to
subclass, see @ref{Inheritance,Inheritance,,eieio}.).  Users of the
application-building interface can then instantiate objects of this
concrete class (using the @code{make-instance} function) and connect
to JSONRPC endpoints using that strategy.

This API has mandatory and optional parts.

@findex jsonrpc-connection-send
To allow its users to initiate JSONRPC contacts (notifications or
requests) or reply to endpoint requests, the subclass must have an
implementation of the @code{jsonrpc-connection-send} method.

@findex jsonrpc-connection-receive
Likewise, for handling the three types of remote contacts (requests,
notifications, and responses to local requests), the transport
implementation must arrange for the function
@code{jsonrpc-connection-receive} to be called after noticing a new
JSONRPC message on the wire (whatever that "wire" may be).

@findex jsonrpc-shutdown
@findex jsonrpc-running-p
Finally, and optionally, the @code{jsonrpc-connection} subclass should
implement the @code{jsonrpc-shutdown} and @code{jsonrpc-running-p}
methods if these concepts apply to the transport.  If they do, then
any system resources (e.g.@: processes, timers, etc.) used to listen for
messages on the wire should be released in @code{jsonrpc-shutdown},
i.e.@: they should only be needed while @code{jsonrpc-running-p} is
non-nil.

@end enumerate

@node Process-based JSONRPC connections
@subsection Process-based JSONRPC connections
@cindex JSONRPC process-based connections

@findex jsonrpc-process-connection
For convenience, the @code{jsonrpc} library comes with a built-in
@code{jsonrpc-process-connection} transport implementation that can
talk to local subprocesses (using the standard input and standard
output); or TCP hosts (using sockets); or any other remote endpoint
that Emacs's process object can represent (@pxref{Processes}).

Using this transport, the JSONRPC messages are encoded on the wire as
plain text and prefaced by some basic HTTP-style enveloping headers,
such as ``Content-Length''.

For an example of an application using this transport scheme on top of
JSONRPC, see the
@uref{https://microsoft.github.io/language-server-protocol/specification,
Language Server Protocol}.

@cindex JSONRPC connection initargs
Along with the mandatory @code{:request-dispatcher} and
@code{:notification-dispatcher} initargs, users of the
@code{jsonrpc-process-connection} class should pass the following
initargs as keyword-value pairs to @code{make-instance}:

@table @code
@item :process
Value must be a live process object or a function of no arguments
producing one such object.  If passed a process object, the object is
expected to contain a pre-established connection; otherwise, the
function is called immediately after the object is made.

@item :on-shutdown
Value must be a function of a single argument, the
@code{jsonrpc-process-connection} object.  The function is called
after the underlying process object has been deleted (either
deliberately by @code{jsonrpc-shutdown}, or unexpectedly, because of
some external cause).
@end table

@node JSONRPC JSON object format
@subsection JSONRPC JSON object format
@cindex JSONRPC object format

JSONRPC JSON objects are exchanged as Lisp plists (@pxref{Property
Lists}): JSON-compatible plists are handed to the dispatcher functions
and, likewise, JSON-compatible plists should be given to
@code{jsonrpc-notify}, @code{jsonrpc-request}, and
@code{jsonrpc-async-request}.

@findex jsonrpc-lambda
To facilitate handling plists, this library makes liberal use of
@code{cl-lib} library (@pxref{Top,cl-lib,,cl,Common Lisp Extensions
for GNU Emacs Lisp}) and suggests (but doesn't force) its clients to
do the same.  A macro @code{jsonrpc-lambda} can be used to create a
lambda for destructuring a JSON-object like in this example:

@example
(jsonrpc-async-request
 myproc :frobnicate `(:foo "trix")
 :success-fn (jsonrpc-lambda (&key bar baz &allow-other-keys)
               (message "Server replied back with %s and %s!"
                        bar baz))
 :error-fn (jsonrpc-lambda (&key code message _data)
             (message "Sadly, server reports %s: %s"
                      code message)))
@end example

@node JSONRPC deferred requests
@subsection Deferred JSONRPC requests
@cindex JSONRPC deferred requests

In many @acronym{RPC} situations, synchronization between the two
communicating endpoints is a matter of correctly designing the RPC
application: when synchronization is needed, requests (which are
blocking) should be used; when it isn't, notifications should suffice.
However, when Emacs acts as one of these endpoints, asynchronous
events (e.g. timer- or process-related) may be triggered while there
is still uncertainty about the state of the remote endpoint.
Furthermore, acting on these events may only sometimes demand
synchronization, depending on the event's specific nature.

@findex :deferred@r{, JSONRPC keyword}
The @code{:deferred} keyword argument to @code{jsonrpc-request} and
@code{jsonrpc-async-request} is designed to let the caller indicate
that the specific request needs synchronization and its actual
issuance may be delayed to the future, until some condition is
satisfied.  Specifying @code{:deferred} for a request doesn't mean it
@emph{will} be delayed, only that it @emph{can} be.  If the request
isn't sent immediately, @code{jsonrpc} will make renewed efforts to
send it at certain key times during communication, such as when
receiving or sending other messages to the endpoint.

@findex jsonrpc-connection-ready-p
Before any attempt to send the request, the application-specific
conditions are checked.  Since the @code{jsonrpc} library can't know
what these conditions are, the program can use the
@code{jsonrpc-connection-ready-p} generic function (@pxref{Generic
Functions}) to specify them.  The default method for this function
returns @code{t}, but you can add overriding methods that return
@code{nil} in some situations, based on the arguments passed to it,
which are the @code{jsonrpc-connection} object (@pxref{JSONRPC
Overview}) and whichever value you passed as the @code{:deferred}
keyword argument.

@node Atomic Changes
@section Atomic Change Groups
@cindex atomic changes

  In database terminology, an @dfn{atomic} change is an indivisible
change---it can succeed entirely or it can fail entirely, but it
cannot partly succeed.  A Lisp program can make a series of changes to
one or several buffers as an @dfn{atomic change group}, meaning that
either the entire series of changes will be installed in their buffers
or, in case of an error, none of them will be.

  To do this for one buffer, the one already current, simply write a
call to @code{atomic-change-group} around the code that makes the
changes, like this:

@example
(atomic-change-group
  (insert foo)
  (delete-region x y))
@end example

@noindent
If an error (or other nonlocal exit) occurs inside the body of
@code{atomic-change-group}, it unmakes all the changes in that buffer
that were during the execution of the body.  This kind of change group
has no effect on any other buffers---any such changes remain.

  If you need something more sophisticated, such as to make changes in
various buffers constitute one atomic group, you must directly call
lower-level functions that @code{atomic-change-group} uses.

@defun prepare-change-group &optional buffer
This function sets up a change group for buffer @var{buffer}, which
defaults to the current buffer.  It returns a handle that
represents the change group.  You must use this handle to activate the
change group and subsequently to finish it.
@end defun

  To use the change group, you must @dfn{activate} it.  You must do
this before making any changes in the text of @var{buffer}.

@defun activate-change-group handle
This function activates the change group that @var{handle} designates.
@end defun

  After you activate the change group, any changes you make in that
buffer become part of it.  Once you have made all the desired changes
in the buffer, you must @dfn{finish} the change group.  There are two
ways to do this: you can either accept (and finalize) all the changes,
or cancel them all.

@defun accept-change-group handle
This function accepts all the changes in the change group specified by
@var{handle}, making them final.
@end defun

@defun cancel-change-group handle
This function cancels and undoes all the changes in the change group
specified by @var{handle}.
@end defun

  Your code should use @code{unwind-protect} to make sure the group is
always finished.  The call to @code{activate-change-group} should be
inside the @code{unwind-protect}, in case the user types @kbd{C-g}
just after it runs.  (This is one reason why
@code{prepare-change-group} and @code{activate-change-group} are
separate functions, because normally you would call
@code{prepare-change-group} before the start of that
@code{unwind-protect}.)  Once you finish the group, don't use the
handle again---in particular, don't try to finish the same group
twice.

  To make a multibuffer change group, call @code{prepare-change-group}
once for each buffer you want to cover, then use @code{nconc} to
combine the returned values, like this:

@example
(nconc (prepare-change-group buffer-1)
       (prepare-change-group buffer-2))
@end example

You can then activate the multibuffer change group with a single call
to @code{activate-change-group}, and finish it with a single call to
@code{accept-change-group} or @code{cancel-change-group}.

  Nested use of several change groups for the same buffer works as you
would expect.  Non-nested use of change groups for the same buffer
will get Emacs confused, so don't let it happen; the first change
group you start for any given buffer should be the last one finished.

@node Change Hooks
@section Change Hooks
@cindex change hooks
@cindex hooks for text changes

  These hook variables let you arrange to take notice of changes in
buffers (or in a particular buffer, if you make them buffer-local).
See also @ref{Special Properties}, for how to detect changes to
specific parts of the text.

  The functions you use in these hooks should save and restore the match
data if they do anything that uses regular expressions; otherwise, they
will interfere in bizarre ways with the editing operations that call
them.

@defvar before-change-functions
This variable holds a list of functions to call when Emacs is about to
modify a buffer.  Each function gets two arguments, the beginning and
end of the region that is about to change, represented as integers.
The buffer that is about to change is always the current buffer when
the function is called.
@end defvar

@defvar after-change-functions
This variable holds a list of functions to call after Emacs modifies a
buffer.  Each function receives three arguments: the beginning and end
of the region just changed, and the length of the text that existed
before the change.  All three arguments are integers.  The buffer that
has been changed is always the current buffer when the function is
called.

The length of the old text is the difference between the buffer
positions before and after that text as it was before the change.  As
for the changed text, its length is simply the difference between the
first two arguments.
@end defvar

  Output of messages into the @file{*Messages*} buffer does not call
these functions, and neither do certain internal buffer changes, such
as changes in buffers created by Emacs internally for certain jobs,
that should not be visible to Lisp programs.

The vast majority of buffer changing primitives will call
@code{before-change-functions} and @code{after-change-functions} in
balanced pairs, once for each change, where the arguments to these
hooks exactly delimit the change being made.  Yet, hook functions
should not rely on this always being the case, because some complex
primitives call @code{before-change-functions} once before making
changes, and then call @code{after-change-functions} zero or more
times, depending on how many individual changes the primitive is
making.  When that happens, the arguments to
@code{before-change-functions} will enclose a region in which the
individual changes are made, but won't necessarily be the minimal such
region, and the arguments to each successive call of
@code{after-change-functions} will then delimit the part of text being
changed exactly.  In general, we advise using either the before- or
the after-change hook, but not both.

@defmac combine-after-change-calls body@dots{}
The macro executes @var{body} normally, but arranges to call the
after-change functions just once for a series of several changes---if
that seems safe.

If a program makes several text changes in the same area of the buffer,
using the macro @code{combine-after-change-calls} around that part of
the program can make it run considerably faster when after-change hooks
are in use.  When the after-change hooks are ultimately called, the
arguments specify a portion of the buffer including all of the changes
made within the @code{combine-after-change-calls} body.

@strong{Warning:} You must not alter the values of
@code{after-change-functions} within
the body of a @code{combine-after-change-calls} form.

@strong{Warning:} if the changes you combine occur in widely scattered
parts of the buffer, this will still work, but it is not advisable,
because it may lead to inefficient behavior for some change hook
functions.
@end defmac

@defmac combine-change-calls beg end body@dots{}
This executes @var{body} normally, except any buffer changes it makes
do not trigger the calls to @code{before-change-functions} and
@code{after-change-functions}.  Instead there is a single call of each
of these hooks for the region enclosed by @var{beg} and @var{end}, the
parameters supplied to @code{after-change-functions} reflecting the
changes made to the size of the region by @var{body}.

The result of this macro is the result returned by @var{body}.

This macro is useful when a function makes a possibly large number of
repetitive changes to the buffer, and the change hooks would otherwise
take a long time to run, were they to be run for each individual
buffer modification.  Emacs itself uses this macro, for example, in
the commands @code{comment-region} and @code{uncomment-region}.

@strong{Warning:} You must not alter the values of
@code{before-change-functions} or @code{after-change-function} within
@var{body}.

@strong{Warning:} You must not make any buffer changes outside of the
region specified by @var{beg} and @var{end}.
@end defmac

@defvar first-change-hook
This variable is a normal hook that is run whenever a buffer is changed
that was previously in the unmodified state.
@end defvar

@defvar inhibit-modification-hooks
If this variable is non-@code{nil}, all of the change hooks are
disabled; none of them run.  This affects all the hook variables
described above in this section, as well as the hooks attached to
certain special text properties (@pxref{Special Properties}) and overlay
properties (@pxref{Overlay Properties}).

Also, this variable is bound to non-@code{nil} while running those
same hook variables, so that by default modifying the buffer from
a modification hook does not cause other modification hooks to be run.
If you do want modification hooks to be run in a particular piece of
code that is itself run from a modification hook, then rebind locally
@code{inhibit-modification-hooks} to @code{nil}.
@end defvar

debug log:

solving 2e7c497f57 ...
found 2e7c497f57 in https://git.savannah.gnu.org/cgit/emacs.git

(*) Git path names are given by the tree(s) the blob belongs to.
    Blobs themselves have no identifier aside from the hash of its contents.^

Code repositories for project(s) associated with this public inbox

	https://git.savannah.gnu.org/cgit/emacs.git

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).