* test/lisp/progmodes/eglot-tests.el (eglot-test-semtok-basic)
(eglot-test-semtok-refontify): Fix tests.

CTAGS.good_update not yet updated.

* lisp/emacs-lisp/package.el (package-install): Delete dead code
resulting from previous change.
* test/lisp/emacs-lisp/package-tests.el
(package-test-install-single): Adjust code to expect
'user-error'

Discussed in
https://lists.gnu.org/archive/html/emacs-devel/2025-12/msg00903.html.

* lisp/progmodes/project.el (project-files) <vc>: Look up the
value of 'project-vc-ignores' inside DIR rather than project root.
This allows this variable to be applied in external dirs as well.
(project-ignores) <vc>: Do likewise.
(project--value-in-dir): Ensure that DIR has a trailing slash.
The caller might pass the value without slash if produced
differently.

* test/lisp/progmodes/project-tests.el
(project-vc-ignores-in-external-directory): New test.
(project-vc-supports-files-in-subdirectory): Update the test,
considering the subtle change in behavior: the directory DIR
directly includes a .dir-locals.el which sets project-vc-ignores,
which wasn't previously applied because it wasn't set in the root.

* lisp/calendar/calendar.el (calendar-redraw)
(calendar-other-month): Make sure that the mode line is updated
after cursor motion in case 'date' is used in
'calendar-mode-line-format'.
(calendar-set-date-style): Delete call to
calendar-update-mode-line because it is called in calendar-draw.
(calendar-generate-window): Delete calls to
calendar-update-mode-line and calendar-cursor-to-visible-date.
It's better for the caller to do it.
(calendar-basic-setup): Update cursor position and mode line.
* lisp/calendar/cal-move.el (calendar-goto-today): Delete
calendar-update-mode-line because calendar-move-hook is called
last.  This is consistent with other cal-move commands.
* test/lisp/calendar/calendar-tests.el
(calendar-test-date-in-mode-line): New test.

Zero-length strings are just 'empty'; 'null' can be confusing in several
ways.

* lisp/subr.el (split-string, string-lines):
* doc/lispref/strings.texi (Creating Strings):
Change argument names from 'omit-nulls' to 'omit-empty'.

* lisp/subr.el (split-string):
Fix quadratic behaviour in (split-string "x:x:x..." ":" nil " +").
General code reorganisation for speed and reduced allocation.
Fix a regexp bug; eg, (split-string "A;B" "," nil ";\\|:")

* test/lisp/subr-tests.el (subr-test-split-string):
More extensive test coverage.

Some of the fixes are to continue to use American
rather than British spelling.
* doc/misc/modus-themes.org (my-modus-themes-engraved-faces):
Fix misspelled ‘:foreground’s.
* etc/themes/modus-themes.el (modus-themes-faces):
Fix misspelled ‘modus-themes-bold’.
* lisp/emacs-lisp/rx.el (rx--normalize-char-pattern):
Rename from rx--normalise-char-pattern.
(rx--optimize-or-args):	Rename from rx--optimise-or-args.
* lisp/frame.el (frame--special-parameters):
Fix misspelled "right-divider-width".
* lisp/net/tramp.el (tramp-fingerprint-prompt-regexp):
Use American spelling “centered”, to match current libfprintf.
* lisp/org/org-fold-core.el (org-fold-core--optimize-for-huge-buffers):
Rename from org-fold-core--optimise-for-huge-buffers.
(org-fold-core-update-optimization):
Rename from org-fold-core-update-optimisation,
leaving an alias behind.
(org-fold-core-remove-optimization):
Rename from org-fold-core-remove-optimisation,
leaving an alias behind.
* lisp/org/org.el (org-advertized-archive-subtree):
This alias is now obsolete.
* lisp/play/zone.el (zone-ignored-buffers):
Fix misspelling of ‘zone--buffer-encrypted-p’.
* lisp/progmodes/csharp-mode.el (csharp-ts-mode-faces):
Fix misspelling of ‘csharp’ group.
* lisp/vc/vc.el (vc-clonable-backends-custom-type):
Rename from vc-cloneable-backends-custom-type,
leaving an alias behind.
* test/lisp/emacs-lisp/bytecomp-tests.el:
(bytecomp-tests--warn-arity-non-compiled-callee):
Rename from bytecomp-tests--warn-arity-noncompiled-callee.
(bytecomp-test-defface-spec): Reword a deliberate misspelling
of “default” that is so common I don’t want it to pollute the
spelling dictionary.
* test/lisp/emacs-lisp/package-vc-tests.el:
(package-vc-tests-preserve-artifacts):
Rename from package-vc-tests-preserve-artifacts.
* test/lisp/eshell/em-prompt-tests.el:
(em-prompt-test/forward-backward-paragraph-1):
Reword a deliberate misspelling of “goodbye” that is so common I
don’t want it to pollute the spelling dictionary.

* lisp/net/tramp-adb.el (tramp-adb-do-ls): New function.
(tramp-adb-handle-file-attributes)
(tramp-adb-handle-directory-files-and-attributes)
(tramp-adb-handle-file-name-all-completions): Use it.  (Bug#80054)