--text follows this line--

- Starting from 'emacs -Q'

- Invoke CPerl mode via 'M-X cperl-mode'.

- Edit (or create) a buffer that has more lines than the display window.

- Open another window (same size), via 'C-x 5 2'.

- Position the view in that second window to the end of the buffer, via
'ESC->'.

- In the first window, near the top of the buffer, enter this string,
the start of a pair of escaped [] brackets within a perl regexp range:

my $x = qr/[\[\

- Enter the second escaped ']':

my $x = qr/[\[\]

When it is entered, a diagnostic like

  Couldn't find end of charclass in a REx, pos=33584

is displayed in the echo area at the bottom of the edit window and then
the other window displaying that buffer is scrolled (repositioned) back
to the same view as the window being edited, outside the user's control,
abandoning its previous position.

The views, the windows, that are repositioned are those of any latter
part of the buffer.

Peculiarly, identical edits in latter portions of the buffer do not
cause a similar repositioning of top-of-buffer views although they do
generate the diagnostic.

This is just one example of how the repositioning happens. In general,
any edit that results in a message being displayed in the echo area
causes the view to be repositioned.

In the cperl source (git cperl-master), it looks like these
diagnostics are generated via elisp's (message) function. Is this
repositioning a side effect of that function?

The repositioning causes problems when it's important to maintain
multiple views of different parts of a large file. It's like shaking
all the bookmarks out of a reference book, then trying to find the
bookmarked places again.

In GNU Emacs 26.3 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.14)
 of 2020-03-26, modified by Debian built on lcy01-amd64-020
Windowing system distributor 'The X.Org Foundation', version 11.0.12009000
System Description:     Ubuntu 20.04.2 LTS

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --enable-libsystemd --with-pop=yes
 --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/26.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/26.3/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils --build
 x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib
 --libexecdir=/usr/lib --localstatedir=/var/lib
 --infodir=/usr/share/info --mandir=/usr/share/man --enable-libsystemd
 --with-pop=yes
 --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/26.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/26.3/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils --with-x=yes
 --with-x-toolkit=gtk3 --with-toolkit-scroll-bars 'CFLAGS=-g -O2
 -fdebug-prefix-map=/build/emacs-mEZBk7/emacs-26.3+1=.
-fstack-protector-strong
 -Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS GLIB
NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM THREADS LIBSYSTEMD LCMS2

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.


Features:
(shadow sort mail-extr emacsbug message rmc puny seq byte-opt gv
bytecomp byte-compile cconv cl-loaddefs cl-lib dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils elec-pair time-date
mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel term/x-win x-win term/common-win x-dnd tool-bar
dnd fontset image regexp-opt fringe tabulated-list replace newcomment
text-mode elisp-mode lisp-mode prog-mode register page menu-bar
rfn-eshadow isearch timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core term/tty-colors frame cl-generic cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese composite charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray minibuffer
cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote threads dbusbind
inotify lcms2 dynamic-setting system-font-setting font-render-setting
move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 94874 11705)
 (symbols 48 20386 1)
 (miscs 40 44 143)
 (strings 32 28402 800)
 (string-bytes 1 746365)
 (vectors 16 13898)
 (vector-slots 8 500864 9876)
 (floats 8 49 231)
 (intervals 56 262 0)
 (buffers 992 11))