GNU Emacs NEWS -- history of user-visible changes.

Copyright (C) 2017-2018 Free Software Foundation, Inc.
See the end of the file for license conditions.

Please send Emacs bug reports to bug-gnu-emacs@gnu.org.
If possible, use M-x report-emacs-bug.

This file is about changes in Emacs version 27.

See file HISTORY for a list of GNU Emacs versions and release dates.
See files NEWS.26, NEWS.25, ..., NEWS.18, and NEWS.1-17 for changes
in older Emacs versions.

You can narrow news to a specific version by calling 'view-emacs-news'
with a prefix argument or by typing C-u C-h C-n.

Temporary note:
+++ indicates that all necessary documentation updates are complete.
    (This means all relevant manuals in doc/ AND lisp doc-strings.)
--- means no change in the manuals is needed.
When you add a new item, use the appropriate mark if you are sure it applies,


* Installation Changes in Emacs 27.1

** The new configure option '--with-json' adds support for JSON using
the Jansson library.  It is on by default; use 'configure
--with-json=no' to build without Jansson support.  The new JSON
functions 'json-serialize', 'json-insert', 'json-parse-string', and
'json-parse-buffer' are typically much faster than their Lisp
counterparts from json.el.

** Emacs has been ported to the -fcheck-pointer-bounds option of GCC.
This causes Emacs to check bounds of some arrays addressed by its
internal pointers, which can be helpful when debugging the Emacs
interpreter or modules that it uses.  If your platform supports it you
can enable it when configuring, e.g., './configure CFLAGS="-g3 -O2
-mmpx -fcheck-pointer-bounds"' on Intel MPX platforms.

** Emacs now normally uses a C pointer type instead of a C integer
type to implement Lisp_Object, which is the fundamental machine word
type internal to the Emacs Lisp interpreter.  This change aims to
catch typos and support -fcheck-pointer-bounds.  The 'configure'
option --enable-check-lisp-object-type is therefore no longer as
useful and so is no longer enabled by default in developer builds,
to reduce differences between developer and production builds.


* Startup Changes in Emacs 27.1

+++
** Emacs can now be configured using an early init file.
The file is called 'early-init.el', in 'user-emacs-directory'.  It is
loaded very early in the startup process: before graphical elements
such as the tool bar are initialized, and before the package manager
is initialized.  The primary purpose is to allow customizing how the
package system is initialized given that initialization now happens
before loading the regular init file (see below).

We recommend against putting any customizations in this file that
don't need to be set up before initializing installed add-on packages,
because the early init file is read too early into the startup
process, and some important parts of the Emacs session, such as
window-system and other GUI features, are not yet set up, which could
make some customization fail to work.

+++
** Installed packages are now activated *before* loading the init file.
This is part of a change intended to eliminate the behavior of
package.el inserting a call to 'package-initialize' into the init
file, which was previously done when Emacs was started.  As a result
of this change, it is no longer necessary to call 'package-initialize'
in your init file.

However, if your init file changes the values of 'package-load-list' or
'package-user-dir', or sets 'package-enable-at-startup' to nil then it won't
work right without some adjustment:
- you can move that code to the early init file (see above), so those settings
  apply before Emacs tries to activate the packages.
- you can use the new 'package-quickstart' so activation of packages does not
  need to pay attention to 'package-load-list' or 'package-user-dir' any more.


* Changes in Emacs 27.1

---
** New variable 'xft-ignore-color-fonts'.
Default t means don't try to load color fonts when using Xft, as they
often cause crashes.  Set it to nil if you really need those fonts.
(Bug#30874)

---
** The new option 'tooltip-resize-echo-area' avoids truncating tooltip text
on GUI frames when tooltips are displayed in the echo area.  Instead,
it resizes the echo area as needed to accommodate the full tool-tip
text.

---
** Show modeline tooltips only if the corresponding action applies.
Customize the option 'mode-line-default-help-echo' to restore the old
behavior where the tooltip text is also shown when the corresponding
action does not apply.

+++
** New hook 'server-after-make-frame-hook'.
This hook is a convenient place to perform initializations in daemon
mode which require GUI features to be available.  One example is
restoration of the previous session using the desktop.el package: put
the call to 'desktop-read' in this hook, if you want the GUI settings
to be restored, or if desktop.el needs to interact with you during
restoration of the session.

+++
** New function 'logcount' calculates an integer's Hamming weight.

+++
** New function 'libxml-available-p'.
This function returns non-nil if libxml support is both compiled in
and available at run time.  Lisp programs should use this function to
detect built-in libxml support, instead of testing for that
indirectly, e.g., by checking that functions like
'libxml-parse-html-region' return nil.

+++
** 'libxml-parse-xml-region' and 'libxml-parse-html' region take
a parameter that's called DISCARD-COMMENTS, but it really only
discards the top-level comment.  Therefore this parameter is now
obsolete, and the new utility function 'xml-remove-comments' can be
used to remove comments before calling the libxml functions to parse
the data.

+++
** The Network Security Manager now allows more fine-grained control
of what checks to run via the `network-security-protocol-checks'
variable.

+++
** Most of the checks for outdated, believed-to-be-weak TLS algorithms
and ciphers are now switched on by default.

+++
** New function 'fill-polish-nobreak-p', to be used in 'fill-nobreak-predicate'.
It blocks line breaking after a one-letter word, also in the case when
this word is preceded by a non-space, but non-alphanumeric character.

+++
** The limit on repetitions in regexps has been raised to 2^16-1.
It was previously limited to 2^15-1.  For example, the following
regular expression was previously invalid, but is now accepted:

   x\{32768\}

---
** The German prefix and postfix input methods now support Capital sharp S.

+++
** New function 'exec-path'.
This function by default returns the value of the corresponding
variable, but can optionally return the equivalent of 'exec-path'
from a remote host.

+++
** The function 'executable-find' supports an optional argument REMOTE.
This triggers to search the program on the remote host as indicated by
'default-directory'.


* Editing Changes in Emacs 27.1

---
** New variable 'x-wait-for-event-timeout'.
This controls how long Emacs will wait for updates to the graphical
state to take effect (making a frame visible, for example).

+++
** New user option 'electric-quote-replace-double'.
This option controls whether '"' is replaced in 'electric-quote-mode',
in addition to other quote characters.  If non-nil, ASCII double-quote
characters that quote text "like this" are replaced by double
typographic quotes, “like this”, in text modes, and in comments in
non-text modes.

---
** 'write-abbrev-file' now includes special properties.
'write-abbrev-file' now writes special properties like ':case-fixed'
for abbrevs that have them.

+++
** The new functions and commands 'text-property-search-forward' and
'text-property-search-backward' have been added.  These provide an
interface that's more like functions like @code{search-forward}.

---
** More commands support noncontiguous rectangular regions, namely
'upcase-dwim', 'downcase-dwim', 'replace-string', 'replace-regexp'.

+++
** When asked to visit a large file, Emacs now offers visiting it literally.
Previously, Emacs would only ask for confirmation before visiting
large files.  Now it also offers a third alternative: to visit the
file literally, as in 'find-file-literally', which speeds up
navigation and editing of large files.


* Changes in Specialized Modes and Packages in Emacs 27.1

** Browse-url

*** The function 'browse-url-emacs' can now visit a URL in selected window.
It now treats the optional 2nd argument to mean that the URL should be
shown in the currently selected window.

** Comint

+++
*** 'C-c .' (comint-insert-previous-argument) no longer interprets '&'.
This feature caused problems when '&&' was present in the previous
command.  Since this command emulates 'M-.' in Bash and zsh, neither
of which treats '&' specially, the feature was removed for
compatibility with these shells.

+++
*** 'comint-insert-previous-argument' can now count arguments from the end.
By default, invoking 'C-c .' with a numeric argument N would copy the
Nth argument, counting from the first one.  But if the new option
'comint-insert-previous-argument-from-end' is non-nil, it will copy
the Nth argument counting from the last one.  Thus 'C-c .' can now
better emulate 'M-.' in both Bash and zsh, since the former counts
from the beginning of the arguments, while the latter counts from the
end.

** Flymake

+++
*** The variable 'flymake-diagnostic-types-alist' is obsolete
You should instead set properties on known diagnostic symbols, like
':error' and ':warning', as demonstrated in the Flymake manual.

*** New customizable variable 'flymake-start-on-save-buffer'
Control whether Flymake starts checking the buffer on save.

*** Flymake and backend functions may exchange hints about buffer changes
This enables more efficient backends.  See the docstring of
'flymake-diagnostic-functions' or the Flymake manual for details.

** Package

*** New 'package-quickstart' feature
When 'package-quickstart' is non-nil, package.el precomputes a big autoloads
file so that activation of packages can be done much faster, which can speed up
your startup significantly.
It also causes variables like package-user-dir and package-load-list to be
consulted when 'package-quickstart-refresh' is run rather than at startup so
you don't need to set them in your early init file.

*** New function 'package-activate-all'.

** Info

---
*** Info can now follow 'file://' protocol URLs.
The 'file://' URLs in Info documents can now be followed by passing
them to the 'browse-url' function, like the other protocols: ftp,
http, and https.  This allows to have references to local HTML files,
for example.

** Ecomplete

*** The ecomplete sorting has changed to a decay-based algorithm.
This can be controlled by the new 'ecomplete-sort-predicate' variable.

*** The 'ecompleterc' file is now placed in ~/.emacs.d/ecompleterc by default
Of course it will still find it if you have it in ~/.ecompleterc

** Gnus

+++
*** A prefix argument to 'gnus-summary-limit-to-score' will limit reverse
Limit to articles with score at below.

*** The function 'gnus-score-find-favorite-words' has been renamed
from 'gnus-score-find-favourite-words'.

---
*** Gmane has been removed as an nnir backend, since Gmane no longer
has a search engine.

+++
*** Splitting mail on common mailing list headers has been added.  See
the concept index in the Gnus manual for the 'match-list' entry.

+++
*** nil is no longer an allowed value for 'mm-text-html-renderer'.

+++
*** A new Gnus summary mode command, 'S A'
('gnus-summary-attach-article') can be used to attach the current
article(s) to a pre-existing Message buffer, or create a new Message
buffer with the article(s) attached.

** erc

---
*** 'erc-button-google-url' has been renamed 'erc-button-search-url'
and its value has been changed to Duck Duck Go.

** eww/shr

*** When opening external links in eww/shr (typically with the
'C-u RET' keystroke on a link), the link will be flashed with the new
'shr-selected-link' face to give the user feedback that the command
has been executed.

** Htmlfontify

*** The functions 'hfy-color', 'hfy-color-vals' and
'hfy-fallback-color-values' and the variables 'hfy-fallback-color-map'
and 'hfy-rgb-txt-color-map' have been renamed from names that used
'colour' instead of 'color'.

+++
** Enriched mode supports the 'charset' text property.
You can add or modify the 'charset' text properties of text using the
Edit->Text Properties->Special Properties menu, or by invoking the
'facemenu-set-charset' command.  Documents in Enriched mode will be
saved with the charset properties, and those properties will be
restored when the file is visited.

** Smtpmail
Authentication mechanisms can be added via external packages, by
defining new cl-defmethod of smtpmail-try-auth-method.

** Footnote-mode

*** Support Hebrew-style footnotes
*** Footnote text lines are now aligned.
Can be controlled via the new variable 'footnote-align-to-fn-text'.

** CSS mode

---
*** A new command 'css-cycle-color-format' for cycling between color
formats (e.g. "black" => "#000000" => "rgb(0, 0, 0)") has been added,
bound to 'C-c C-f'.

---
*** CSS mode, SCSS mode, and Less CSS mode now have support for Imenu.

** SGML mode

---
*** 'sgml-quote' now handles double quotes and apostrophes
when escaping text and in addition all numeric entities when
unescaping text.

** Dired

+++
*** The new user option 'dired-create-destination-dirs' controls whether
'dired-do-copy' and 'dired-rename-file' should create non-existent
directories in the destination.

** Help

---
*** Output format of 'C-h l' (view-lossage) has changed.
For convenience, 'view-lossage' now displays the last keystrokes
and commands in the same format as the edit buffer of
'edit-last-kbd-macro'.  This makes it possible to copy the lines from
the buffer generated by 'view-lossage' to the "*Edit Macro*" buffer
created by 'edit-last-kbd-macro', and to save the macro by 'C-c C-c'.

---
*** The list of help commands produced by 'C-h C-h' ('help-for-help')
can now be searched via 'C-s'.

** Ibuffer

---
*** New filter ibuffer-filter-by-process; bound to '/E'.

** Search and Replace

+++
*** New isearch bindings.

'C-M-w' in isearch changed from isearch-del-char to the new function
isearch-yank-symbol-or-char.  isearch-del-char is now bound to
'C-M-d'.

+++
*** 'search-exit-option' provides new options 'move' and 'shift-move'
to extend the search string by yanking text that ends at the new
position after moving point in the current buffer.  'shift-move'
extends the search string by motion commands while holding down
the shift key.

---
*** Isearch now remembers the regexp-based search mode for words/symbols
and case-sensitivity together with search strings in the search ring.

** Edebug

+++
*** The runtime behavior of Edebug's instrumentation can be changed
using the new variables 'edebug-behavior-alist',
'edebug-after-instrumentation-function' and
'edebug-new-definition-function'.  Edebug's behavior can be changed
globally or for individual definitions.

** Enhanced xterm support

*** New variable 'xterm-set-window-title' controls whether Emacs sets
the XTerm window title.  This feature is experimental and is disabled
by default.

** Gamegrid

** grep

+++
*** rgrep, lgrep and zrgrep now hide part of the command line
that contains a list of ignored directories and files.
Clicking on the button with ellipsis unhides it.
The abbreviation can be disabled by the new option
'grep-find-abbreviate'.  The new command
'grep-find-toggle-abbreviation' toggles it interactively.

** ERT

+++
*** New variable 'ert-quiet' allows to make ERT output in batch mode
less verbose by removing non-essential information.

---
*** Gamegrid now determines its default glyph size based on display
dimensions, instead of always using 16 pixels.  As a result, Tetris,
Snake and Pong are more playable on HiDPI displays.

** Filecache

---
*** Completing filenames in the minibuffer via 'C-TAB' now uses the
styles as configured by the variable 'completion-styles'.

** New macros 'thunk-let' and 'thunk-let*'.
These macros are analogue to 'let' and 'let*', but create bindings that
are evaluated lazily.

** next-error

+++
*** New customizable variable 'next-error-find-buffer-function'.
The value should be a function that determines how to find the
next buffer to be used by 'next-error' and 'previous-error'.  The
default is to use the last buffer that navigated to the current
error.

+++
*** New command 'next-error-select-buffer'.
It can be used to set any buffer as the next one to be used by
'next-error' and 'previous-error'.

** nxml-mode

---
*** The default value of 'nxml-sexp-element-flag' is now t.
This means that pressing C-M-SPACE now selects the entire tree by
default, and not just the opening element.

** Eshell

---
*** Expansion of history event designators is disabled by default.
To restore the old behavior, use

    (add-hook 'eshell-expand-input-functions
              #'eshell-expand-history-references)

---
*** The function 'eshell-uniquify-list' has been renamed from
'eshell-uniqify-list'.

*** The function eshell/kill is now able to handle signal switches.
Previously eshell/kill would fail if provided a kill signal to send to the
process.  It now accepts signals specified either by name or by its number.

** Shell

---
*** Program name completion inside remote shells works now as expected.

** Pcomplete
*** The function 'pcomplete-uniquify-list' has been renamed from
'pcomplete-uniqify-list'.

** Auth-source

---
*** The Secret Service backend supports the :create key now.

** Tramp

+++
*** New connection method "owncloud", which allows to access OwnCloud
or NextCloud hosted files and directories.

+++
*** Connection methods "obex" and "synce" are removed, because they
are obsoleted in GVFS.

+++
*** Validated passwords are saved by auth-source backends which support this.

+++
*** The user option 'tramp-ignored-file-name-regexp' allows to disable
Tramp for some look-alike remote file names.

---
** The options.el library has been removed.
It was obsolete since Emacs 22.1, replaced by customize.

** The tls.el and starttls.el libraries are now marked obsolete.
Use of built-in libgnutls based functionality (described in the Emacs
GnuTLS manual) is recommended instead.


** Message

+++
*** Messages can now be systematically encrypted
when the PGP keyring contains a public key for every recipient.  To
achieve this, add 'message-sign-encrypt-if-all-keys-available' to
'message-send-hook'.

---
*** When replying a message that have addresses on the form
'"foo@bar.com" <foo@bar.com>', Message will elide the repeated "name"
from the address field in the response.

---
*** The default of 'message-forward-as-mime' has changed from t to nil
as it has been reported that many recipients can't read forwards that
are formatted as MIME digests.

+++
*** 'message-forward-included-headers' has changed its default to
exclude most headers when forwarding.

** EasyPG

---
*** 'epa-pinentry-mode' is renamed to 'epg-pinentry-mode'.
It now applies to epg functions as well as epa functions.

---
*** The alias functions 'epa--encode-coding-string',
'epa--decode-coding-string', and 'epa--select-safe-coding-system' have
been removed.  Use 'encode-coding-string', 'decode-coding-string', and
'select-safe-coding-system' instead.

** Rmail

+++
*** New user option 'rmail-output-reset-deleted-flag'.
If this option is non-nil, messages appended to an output file by the
'rmail-output' command have their Deleted flag reset.

*** The command 'rmail-summary-by-senders' with an empty argument
selects the messages to summarize with a regexp that matches the
sender of the current message.

* New Modes and Packages in Emacs 27.1

+++
** Emacs can now visit files in archives as if they were directories.
This feature uses Tramp and works only on systems which support GVFS,
i.e. GNU/Linux, roughly spoken.  See the chapter "(tramp) Archive file
names" in the Tramp manual for full documentation of these facilities.

+++
** New library for writing JSONRPC applications (https://jsonrpc.org)
The 'jsonrpc' library enables writing Emacs Lisp applications that
rely on this protocol.  Since the protocol is designed to be
transport-agnostic, the library provides an API to implement new
transport strategies as well as a separate API to use them.  A
transport implementation for process-based communication, such as is
used by the Language Server Protocol (LSP), is readily available.


* Incompatible Lisp Changes in Emacs 27.1

---
** Just loading a theme's file no longer activates the theme's settings.
Loading a theme with 'M-x load-theme' still activates the theme, as it
did before.  However, loading the theme's file with "M-x load-file",
or using 'require' or 'load' in a Lisp program, doesn't actually apply
the theme's settings until you either invoke 'M-x enable-theme' or
type 'M-x load-theme'.  (In a Lisp program, calling 'enable-theme' or
invoking 'load-theme' with NO-ENABLE argument omitted or nil has the
same effect of activating a theme whose file has been loaded.)  The
special case of the 'user' theme is an exception: it is frequently
used for ad-hoc customizations, so the settings of that theme are by
default applied immediately.

The variable 'custom--inhibit-theme-enable' controls this behavior;
its default value changed in Emacs 27.1.

** The 'repetitions' argument of 'benchmark-run' can now also be a variable.
** The FILENAME argument to 'file-name-base' is now mandatory and no
longer defaults to 'buffer-file-name'.

---
** The function 'eldoc-message' now accepts a single argument.
Programs that called it with multiple arguments before should pass
them through 'format' first.  Even that is discouraged: for ElDoc
support, you should set 'eldoc-documentation-function' instead of
calling 'eldoc-message' directly.

** Old-style backquotes now generate an error.  They have been
generating warnings for a decade.  To interpret old-style backquotes
as new-style, bind the new variable 'force-new-style-backquotes' to t.

** Defining a Common Lisp structure using 'cl-defstruct' or
'cl-struct-define' whose name clashes with a builtin type (e.g.,
'integer' or 'hash-table') now signals an error.

** When formatting a floating-point number as an octal or hexadecimal
integer, Emacs now signals an error if the number is too large for the
implementation to format (Bug#30408).

+++
** The Lisp reader now signals an overflow for plain decimal integers
that do not end in '.' and are outside Emacs range.  Formerly the Lisp
reader silently converted them to floating-point numbers, and signaled
overflow only for integers with a radix that are outside machine range.
To get the old behavior, set the new, experimental variable
read-integer-overflow-as-float to t and please email
30408@debbugs.gnu.org if you need that.  (Bug#30408).

---
** Some functions and variables obsolete since Emacs 22 have been removed:
archive-mouse-extract, assoc-ignore-case, assoc-ignore-representation,
backward-text-line, blink-cursor, bookmark-exit-hooks,
comint-use-prompt-regexp-instead-of-fields, compilation-finish-function,
count-text-lines, cperl-vc-header-alist, custom-face-save-command,
cvs-display-full-path, cvs-fileinfo->full-path, delete-frame-hook,
derived-mode-class, describe-char-after, describe-project,
desktop-basefilename, desktop-buffer-handlers, desktop-buffer-misc-functions,
desktop-buffer-modes-to-save, desktop-enable, desktop-load-default,
dired-omit-files-p, disabled-command-hook, dungeon-mode-map,
electric-nroff-mode, electric-nroff-newline, electric-perl-terminator,
focus-frame, forward-text-line, generic-define-mswindows-modes,
generic-define-unix-modes, generic-font-lock-defaults, goto-address-at-mouse,
highlight-changes-colours, ibuffer-elide-long-columns, ibuffer-hooks,
ibuffer-mode-hooks, icalendar-convert-diary-to-ical,
icalendar-extract-ical-from-buffer, imenu-always-use-completion-buffer-p,
ipconfig-program, ipconfig-program-options, isearch-lazy-highlight-cleanup,
isearch-lazy-highlight-initial-delay, isearch-lazy-highlight-interval,
isearch-lazy-highlight-max-at-a-time, iswitchb-use-fonts,
latin1-char-displayable-p, mouse-wheel-click-button, mouse-wheel-down-button,
mouse-wheel-up-button, new-frame, pascal-outline, process-kill-without-query,
recentf-menu-append-commands-p, rmail-pop-password,
rmail-pop-password-required, savehist-load, set-default-font,
spam-list-of-processors, speedbar-add-ignored-path-regexp,
speedbar-buffers-line-path, speedbar-ignored-path-expressions,
speedbar-ignored-path-regexp, speedbar-line-path, speedbar-path-line,
timer-set-time-with-usecs, tooltip-gud-display, tooltip-gud-modes,
tooltip-gud-toggle-dereference, unfocus-frame, unload-hook-features-list,
update-autoloads-from-directories, vc-comment-ring, vc-comment-ring-index,
vc-comment-search-forward, vc-comment-search-reverse, vc-comment-to-change-log,
vc-diff-switches-list, vc-next-comment, vc-previous-comment, view-todo,
x-lost-selection-hooks, x-sent-selection-hooks.

---
** Further functions and variables obsolete since Emacs 24 have been removed:
default-directory-alist, dired-default-directory,
dired-default-directory-alist, dired-enable-local-variables,
dired-hack-local-variables, dired-local-variables-file, dired-omit-here-always.

** The function 'display-buffer-in-major-side-window' no longer exists.
It has been renamed as internal function 'window--make-major-side-window',
however applications should instead call 'display-buffer-in-side-window'
(passing the SIDE and SLOT parameters as elements of ALIST).  This approach
is backwards-compatible with versions of Emacs in which the old function
exists.  See the node "Displaying Buffers in Side Windows" in the ELisp
manual for more details.

* Lisp Changes in Emacs 27.1

** define-minor-mode automatically documents the meaning of ARG

+++
** The function 'recenter' now accepts an additional optional argument.
By default, calling 'recenter' will not redraw the frame even if
'recenter-redisplay' is non-nil.  Call 'recenter' with the new second
argument non-nil to force redisplay per 'recenter-redisplay's value.

+++
** New functions 'major-mode-suspend' and 'major-mode-restore'.
Use them when switching temporarily to another major mode, e.g. for
'hexl-mode', or to switch between 'c-mode' and 'image-mode' in XPM.

+++
** New macro 'dolist-with-progress-reporter'.
This works like 'dolist', but reports progress similar to
'dotimes-with-progress-reporter'.

+++
** New hook 'after-delete-frame-functions'.
This works like 'delete-frame-functions', but runs after the frame to
be deleted has been made dead and removed from the frame list.

+++
** New frame focus state inspection interface.
The hooks 'focus-in-hook' and 'focus-out-hook' are now obsolete.
Instead, attach to 'after-focus-change-function' using 'add-function'
and inspect the focus state of each frame using 'frame-focus-state'.

+++
** Emacs now requests and recognizes focus-change notifications from TTYs.
On terminal emulators that support the feature, Emacs can now support
'focus-in-hook' and 'focus-out-hook' for TTY frames.

+++
** Window-specific face remapping.
Face specifications (of the kind used in 'face-remapping-alist')
now support filters, allowing faces to vary between different windows
displaying the same buffer.  See the Info node "Face Remapping" of the
Emacs Lisp Reference manual for more detail.

+++
** New function assoc-delete-all.

+++
** New function 'string-distance' to calculate the Levenshtein distance
between two strings.

** 'print-quoted' now defaults to t, so if you want to see
(quote x) instead of 'x you will have to bind it to nil where applicable.

** To avoid confusion caused by "smart quotes", the reader signals an
error when reading Lisp symbols which begin with one of the following
quotation characters: ‘’‛“”‟〞＂＇.  A symbol beginning with such a
character can be written by escaping the quotation character with a
backslash.  For example:

    (read "‘smart") => (invalid-read-syntax "strange quote" "‘")
    (read "\\‘smart") == (intern "‘smart")

+++
** Omitting variables after '&optional' and '&rest' is now allowed.
For example (defun foo (&optional)) is no longer an error.  This is
sometimes convenient when writing macros.  See the ChangeLog entry
titled "Allow '&rest' or '&optional' without following variable
(Bug#29165)" for a full listing of which arglists are accepted across
versions.

** Internal parsing commands now use 'syntax-ppss' and disregard
'open-paren-in-column-0-is-defun-start'.  This affects mostly things like
'forward-comment', 'scan-sexps', and 'forward-sexp' when parsing backward.
The new variable 'comment-use-syntax-ppss' can be set to nil to recover the old
behavior if needed.

** The 'server-name' and 'server-socket-dir' variables are set when a
socket has been passed to Emacs (Bug#24218).

---
** The 'file-system-info' function is now available on all platforms.
instead of just Microsoft platforms.  This fixes a 'get-free-disk-space'
bug on OS X 10.8 and later (Bug#28639).

+++
** 'memory-limit' now returns a better estimate of memory consumption.

+++
** New macro 'combine-change-calls' arranges to call the change hooks
('before-change-functions' and 'after-change-functions') just once
each around a sequence of lisp forms, given a region.  This is
useful when a function makes a possibly large number of repetitive
changes and the change hooks are time consuming.

---
** The function 'get-free-disk-space' returns now a non-nil value for
remote systems, which support this check.

+++
** The function 'make-string' accepts an additional optional argument.
If the optional third argument is non-nil, 'make-string' will produce
a multibyte string even if its second argument is an ASCII character.

** (format "%d" X) no longer mishandles a floating-point number X that
does not fit in a machine integer (Bug#30408).

** New JSON parsing and serialization functions 'json-serialize',
'json-insert', 'json-parse-string', and 'json-parse-buffer'.  These
are implemented in C using the Jansson library.

** Mailcap

---
*** The new function 'mailcap-file-name-to-mime-type' has been added.
It's a simple convenience function for looking up MIME types based on
file name extensions.

*** The default way the list of possible external viewers for MIME
types is sorted and chosen has changed.  Earlier, the most specific
viewer was chosen, even if there was a general override in ~/.mailcap.
For instance, if /etc/mailcap has an entry for image/gif, that one
will be chosen even if you have an entry for image/* in your
~/.mailcap file.  But with the new method, entries from ~/.mailcap
overrides all system and Emacs-provided defaults.  To get the old
method back, set 'mailcap-prefer-mailcap-viewers' to nil.

** URL

*** The file: handler no longer looks for index.html in directories if
you ask it for a file:///dir URL.  Since this is a low-level library,
such decisions (if they are to be made at all) are left to
higher-level functions.

** image-mode

*** image-mode started using ImageMagick by default for all images
some years back.  It now respects 'imagemagick-types-inhibit' as a way
to disable that.

+++
** The new function 'read-answer' accepts either long or short answers
depending on the new customizable variable 'read-answer-short'.

** The function 'load' now behaves correctly when loading modules.
Specifically, it puts the module name into 'load-history', prints
loading messages if requested, and protects against recursive loads.

+++
** The function 'read-variable' now uses its own history list.
The history of variable names read by 'read-variable' is recorded in
the new variable 'custom-variable-history'.

---
** The function 'string-to-unibyte' is no longer declared obsolete.
We have found that there are legitimate use cases for this function,
where there's no better alternative.  We believe that the incorrect
uses of this function all but disappeared by now, so we are
un-obsoleting it.


* Changes in Emacs 27.1 on Non-Free Operating Systems

---
** Battery status is now supported in all Cygwin builds.
Previously it was supported only in the Cygwin-w32 build.

** Emacs now handles key combinations involving the macOS "command"
and "option" modifier keys more correctly.

** The special handling of 'frame-title-format' on NS where setting it
to 't' would enable the macOS proxy icon has been replaced with a
separate variable, 'ns-use-proxy-icon'.  'frame-title-format' will now
work as on other platforms.

---
** New primitive 'w32-read-registry'.
This primitive lets Lisp programs access the MS-Windows Registry by
retrieving values stored under a given key.  It is intended to be used
for supporting features such as XDG-like location of important files
and directories.

+++
** The default value of 'w32-pipe-read-delay' is now zero.
This speeds up reading output from sub-processes that produce a lot of
data.

This variable may need to be non-zero only when running DOS programs
as Emacs subprocesses, which by now is not supported on modern
versions of MS-Windows.  Set this variable to 50 if for some reason
you need the old behavior (and please report such situations to Emacs
developers).


----------------------------------------------------------------------
This file is part of GNU Emacs.

GNU Emacs is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.


Local variables:
coding: utf-8
mode: outline
paragraph-separate: "[ 	]*$"
end: