Merge from origin/emacs-27

2f9bfaef21 (origin/emacs-27) ; Fix last change
520fd3e728 * lisp/env.el (substitute-env-vars): Doc fix.  (Bug#40948)
85544f8ef5 * lisp/isearch.el: Fix lazy-highlighting and lazy-counting...
d83cc05a73 Fix error in ERC when 'erc-server-coding-system' is custom...
16fed05ba8 Avoid crashes on TTY frames with over-long compositions
0278741676 Fix typo in custom.texi
9f5ae717fb * test/lisp/simple-tests.el (with-shell-command-dont-erase...
1f76a16ed3 * lisp/image-mode.el (image-mode-map): Update menu items.
f0e1bf56f0 Fix bugs in tab-bar and tab-line and mention remaining fea...
f0b9f18457 Make shell-command tests fit for tcsh.
68f4a740a1 Remove doc duplication
ac31cd384c * etc/NEWS: Fix inconsistencies.

# Conflicts:
#	etc/NEWS

4 files changed, 66 insertions, 8 deletions

diff --git a/doc/emacs/custom.texi b/doc/emacs/custom.texi
index e7e879065ed..406f0c96c1f 100644
--- a/doc/emacs/custom.texi
+++ b/doc/emacs/custom.texi
@@ -755,7 +755,7 @@ non-@code{nil} value).  If you set a variable using the customization
 buffer, you need not worry about giving it an invalid type: the
 customization buffer usually only allows you to enter meaningful
 values.  When in doubt, use @kbd{C-h v} (@code{describe-variable}) to
-check the variable's documentation string to see kind of value it
+check the variable's documentation string to see what kind of value it
 expects (@pxref{Examining}).
 
 @menu
diff --git a/doc/emacs/frames.texi b/doc/emacs/frames.texi
index d9373b8bc78..8f448e1aedc 100644
--- a/doc/emacs/frames.texi
+++ b/doc/emacs/frames.texi
@@ -1266,7 +1266,7 @@ Note that the Tab Bar is different from the Tab Line (@pxref{Tab Line}).
 Whereas tabs on the Tab Line at the top of each window are used to
 switch between buffers, tabs on the Tab Bar at the top of each frame
 are used to switch between window configurations containing several
-windows.
+windows with buffers.
 
 @findex tab-bar-mode
   To toggle the use of tab bars, type @kbd{M-x tab-bar-mode}.  This
@@ -1324,6 +1324,10 @@ current before calling the command that adds a new tab.
 To start a new tab with other buffers, customize the variable
 @code{tab-bar-new-tab-choice}.
 
+@vindex tab-bar-new-tab-to
+  The variable @code{tab-bar-new-tab-to} defines where to place a new tab.
+By default, a new tab is added on the right side of the current tab.
+
   The following commands can be used to delete tabs:
 
 @table @kbd
@@ -1331,7 +1335,8 @@ To start a new tab with other buffers, customize the variable
 @kindex C-x t 0
 @findex tab-close
 Close the selected tab (@code{tab-close}).  It has no effect if there
-is only one tab.
+is only one tab, unless the variable @code{tab-bar-close-last-tab-choice}
+is customized to a non-default value.
 
 @item C-x t 1
 @kindex C-x t 1
@@ -1339,6 +1344,14 @@ is only one tab.
 Close all tabs on the selected frame, except the selected one.
 @end table
 
+@vindex tab-bar-close-tab-select
+  The variable @code{tab-bar-close-tab-select} defines what tab to
+select after closing the current tab.  By default, it selects
+a recently used tab.
+
+@findex tab-undo
+  The command @code{tab-undo} restores the last closed tab.
+
   The following commands can be used to switch between tabs:
 
 @table @kbd
@@ -1358,22 +1371,60 @@ switches back to the previous Nth tab.
 Switch to the previous tab.  With a positive numeric argument N, it
 switches to the previous Nth tab; with a negative argument −N, it
 switches back to the next Nth tab.
+
+@item C-x t @key{RET} @var{tabname} @key{RET}
+Switch to the tab by its name, with completion on all tab names.
+Default values are tab names sorted by recency, so you can use
+@kbd{M-n} (@code{next-history-element}) to get the name of the last
+visited tab, the second last, and so on.
+
+@item @var{modifier}-@var{tabnumber}
+@findex tab-select
+Switch to the tab by its number.  After customizing the variable
+@code{tab-bar-select-tab-modifiers} to specify a @var{modifier} key, you
+can select a tab by its ordinal number using the specified modifier in
+combination with the tab number to select.  To display the tab number
+alongside the tab name, you can customize another variable
+@code{tab-bar-tab-hints}.  This will help you to decide what key to press
+to select the tab by its number.
+
+@item @var{modifier}-@kbd{0}
+@findex tab-recent
+Switch to the recent tab.  The key combination is the modifier key
+defined by @code{tab-bar-select-tab-modifiers} and the key @kbd{0}.
+With a numeric argument N, switch to the Nth recent tab.
 @end table
 
   The following commands can be used to operate on tabs:
 
 @table @kbd
 @item C-x t r @var{tabname} @key{RET}
+@findex tab-rename
 Rename the current tab to @var{tabname}.  You can control the
 programmatic name given to a tab by default by customizing the
 variable @code{tab-bar-tab-name-function}.
 
 @item C-x t m
+@findex tab-move
 Move the current tab N positions to the right with a positive numeric
-argument N.  With a negative argument −N, it moves the current tab
+argument N.  With a negative argument −N, move the current tab
 N positions to the left.
 @end table
 
+@findex tab-bar-history-mode
+  You can enable @code{tab-bar-history-mode} to remember window
+configurations used in every tab, and restore them.
+
+@table @kbd
+@item tab-bar-history-back
+Restore a previous window configuration used in the current tab.
+This navigates back in the history of window configurations.
+
+@item tab-bar-history-forward
+Cancel restoration of the previous window configuration.
+This navigates forward in the history of window configurations.
+@end table
+
 @node Dialog Boxes
 @section Using Dialog Boxes
 @cindex dialog boxes
diff --git a/doc/emacs/windows.texi b/doc/emacs/windows.texi
index cb5e9bce4d1..4c67660b92d 100644
--- a/doc/emacs/windows.texi
+++ b/doc/emacs/windows.texi
@@ -628,8 +628,16 @@ Selecting the previous window-local tab is the same as typing @kbd{C-x
 same as @kbd{C-x @key{RIGHT}} (@code{next-buffer}).  Both commands
 support a numeric prefix argument as a repeat count.
 
+You can customize the variable @code{tab-line-tabs-function} to define
+the preferred contents of the tab line.  By default, it displays all
+buffers previously visited in the window, as described above.  But you
+can also set it to display a list of buffers with the same major mode
+as the current buffer, or to display buffers grouped by their major
+mode, where clicking on the mode name in the first tab displays a list
+of all major modes where you can select another group of buffers.
+
 Note that the Tab Line is different from the Tab Bar (@pxref{Tab Bars}).
 Whereas tabs on the Tab Bar at the top of each frame are used to
-switch between window configurations containing several windows,
+switch between window configurations containing several windows with buffers,
 tabs on the Tab Line at the top of each window are used to switch
-between buffers.
+between buffers in the window.
diff --git a/doc/lispref/objects.texi b/doc/lispref/objects.texi
index d35a9ace572..cd037d663da 100644
--- a/doc/lispref/objects.texi
+++ b/doc/lispref/objects.texi
@@ -2406,8 +2406,7 @@ call @code{(make-string 3 ?a)} yields a mutable string that can be
 changed via later calls to @code{aset}.
 
   A mutable object can become constant if it is part of an expression
-that is evaluated, because a program should not modify an object
-that is being evaluated.  The reverse does not occur: constant objects
+that is evaluated.  The reverse does not occur: constant objects
 should stay constant.
 
   Trying to modify a constant variable signals an error