Add documentation for window-tool-bar package

Also change window-tool-mode to not pay attention to if
tool-bar-map has a buffer local value or not as that made the
documentation complicated.  Documentation added in Emacs manual,
Elisp manual, package commentary, and docstrings.  Also extend
window-tool-bar support to Emacs 27 and newer.  (bug#68765)

* doc/emacs/emacs.texi (Top):
* doc/emacs/frames.texi (Menu Bars):
* doc/emacs/glossary.texi (Glossary):
* doc/emacs/modes.texi (Minor Modes):
* doc/emacs/windows.texi (Windows, Tab Line): Mention Window
Tool Bar.
(Window Tool Bar): New documentation.
* doc/lispref/elisp.texi (Top):
* doc/lispref/modes.texi (Mode Line Format, Mode Line Basics)
(Mode Line Data): Mention Tab Lines.
(Tab Lines): New documentation.
* etc/NEWS: Mention newly added variable and package.
* lisp/window-tool-bar.el (window-tool-bar-mode): Don't display
tool bar when tool-bar-map is nil.
* lisp/window-tool-bar.el (tool-bar-always-show-default): Define
variable for older Emacs versions.

7 files changed, 106 insertions, 22 deletions

diff --git a/doc/emacs/emacs.texi b/doc/emacs/emacs.texi
index 7d77f13ab21..8246041fb95 100644
--- a/doc/emacs/emacs.texi
+++ b/doc/emacs/emacs.texi
@@ -529,6 +529,7 @@ Multiple Windows
 * Temporary Displays::  Displaying non-editable buffers.
 * Window Convenience::  Convenience functions for window handling.
 * Tab Line::            Window tab line.
+* Window Tool Bar::     A tool bar that is attached to windows.
 
 Displaying a Buffer in a Window
 
diff --git a/doc/emacs/frames.texi b/doc/emacs/frames.texi
index 6c62fde4ffb..e1fbf9768af 100644
--- a/doc/emacs/frames.texi
+++ b/doc/emacs/frames.texi
@@ -1295,16 +1295,22 @@ menus' visual appearance.
 @node Tool Bars
 @section Tool Bars
 @cindex tool bar mode
+@cindex tool bar, attached to frame
 @cindex mode, Tool Bar
 @cindex icons, toolbar
 
-  On graphical displays, Emacs puts a @dfn{tool bar} at the top of
-each frame, just below the menu bar.  This is a row of icons which you
-can click on with the mouse to invoke various commands.
+  On graphical displays, Emacs puts a @dfn{tool bar} at the top of each
+frame, just below the menu bar.  This is a row of buttons with icons
+which you can click on with the mouse to invoke various commands.  Emacs
+can also optionally display a tool bar at the top of each window
+(@pxref{Window Tool Bar}).
 
+@vindex tool-bar-always-show-default
   The global (default) tool bar contains general commands.  Some major
 modes define their own tool bars; whenever a buffer with such a major
-mode is current, the mode's tool bar replaces the global tool bar.
+mode is current, the mode's tool bar replaces the global tool bar.  To
+prevent this replacement from happening, customize the variable
+@code{tool-bar-always-show-default}.
 
 @findex tool-bar-mode
 @vindex tool-bar-mode
diff --git a/doc/emacs/glossary.texi b/doc/emacs/glossary.texi
index 344e4831f36..e245cb81754 100644
--- a/doc/emacs/glossary.texi
+++ b/doc/emacs/glossary.texi
@@ -1436,10 +1436,12 @@ particular appearance or behavior.  For example, you might use a theme
 for your favorite set of faces (q.v.).
 
 @item Tool Bar
-The tool bar is a line (sometimes multiple lines) of icons at the top
-of an Emacs frame.  Clicking on one of these icons executes a command.
-You can think of this as a graphical relative of the menu bar (q.v.).
-@xref{Tool Bars}.
+The tool bar is a line (sometimes multiple lines) of buttons with icons
+at the top of an Emacs frame.  Clicking on one of these buttons executes
+a command.  You can think of this as a graphical relative of the menu
+bar (q.v.).  @xref{Tool Bars}.  There is also a window tool bar that
+behaves similarly, but is at the top of an Emacs window.  @xref{Window
+Tool Bar}.
 
 @anchor{Glossary---Tooltips}
 @item Tooltips
diff --git a/doc/emacs/modes.texi b/doc/emacs/modes.texi
index 2776dc72a27..1321464014d 100644
--- a/doc/emacs/modes.texi
+++ b/doc/emacs/modes.texi
@@ -296,6 +296,9 @@ but the tool bar is only displayed on graphical terminals.  @xref{Tool
 Bars}.
 
 @item
+Window Tool Bar mode gives windows a tool bar.  @xref{Window Tool Bar}.
+
+@item
 Tab Bar mode gives each frame a tab bar.  @xref{Tab Bars}.
 
 @item
diff --git a/doc/emacs/windows.texi b/doc/emacs/windows.texi
index ad2225b5922..80394e0e571 100644
--- a/doc/emacs/windows.texi
+++ b/doc/emacs/windows.texi
@@ -22,6 +22,7 @@ one frame.
 * Displaying Buffers::  How Emacs picks a window for displaying a buffer.
 * Window Convenience::  Convenience functions for window handling.
 * Tab Line::            Window tab line.
+* Window Tool Bar::     A tool bar that is attached to windows.
 @end menu
 
 @node Basic Window
@@ -689,3 +690,45 @@ Whereas tabs on the Tab Bar at the top of each frame are used to
 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 in the window.
+
+Also note that the tab line displays in the same space as the window
+tool bar, so only one of these can be display at a time unless you
+customize the value of @code{tab-line-format} in Lisp.  In this case,
+add @code{(:eval (tab-line-format))} to @code{tab-line-format}.
+@xref{Mode Line Format,,, elisp, The Emacs Lisp Reference Manual}.
+
+
+@node Window Tool Bar
+@section Window Tool Bar
+
+@cindex window tool bar
+@cindex mode, window tool bar
+@cindex tool bar, attached to window
+
+@findex global-window-tool-bar-mode
+  The command @code{global-window-tool-bar-mode} toggles the display of
+a tool bar at the top of each window.  When enabled, multiple windows
+can display their own tool bar simultaneously.  To conserve space, a
+window tool bar is hidden if there are no buttons to show, i.e. if
+@code{tool-bar-map} is @code{nil}.
+
+@findex window-tool-bar-mode
+If you want to toggle the display of a window tool bar for only some
+buffers, run the command @code{window-tool-bar-mode} in those buffers.
+This is useful to put in a mode hook.  For example, if you want the window
+tool bar to appear only for buffers that do not represent files and have
+a custom tool bar, you could add the following code to your init file
+(@pxref{Init File}):
+
+@example
+(add-hook 'special-mode-hook 'window-tool-bar-mode)
+@end example
+
+Emacs can also display a single tool bar at the top of frames
+(@pxref{Tool Bars}).
+
+Note that the window tool bar displays in the same space as the tab
+line, so only one of these can be display at a time unless you customize
+the value of @code{tab-line-format} in Lisp.  In this case, add
+@code{(:eval (window-tool-bar-string))} to @code{tab-line-format}.
+@xref{Mode Line Format,,, elisp, The Emacs Lisp Reference Manual}.
diff --git a/doc/lispref/elisp.texi b/doc/lispref/elisp.texi
index 339272d1f05..1059d0dcf61 100644
--- a/doc/lispref/elisp.texi
+++ b/doc/lispref/elisp.texi
@@ -925,6 +925,7 @@ Mode Line Format
 * %-Constructs::            Putting information into a mode line.
 * Properties in Mode::      Using text properties in the mode line.
 * Header Lines::            Like a mode line, but at the top.
+* Tab Lines::               A line that is above the header line.
 * Emulating Mode Line::     Formatting text as the mode line would.
 
 Font Lock Mode
diff --git a/doc/lispref/modes.texi b/doc/lispref/modes.texi
index cf67b319924..f3d4f5347b3 100644
--- a/doc/lispref/modes.texi
+++ b/doc/lispref/modes.texi
@@ -2074,14 +2074,14 @@ their previous values/states (using the companion function
 line at the bottom, which displays status information about the buffer
 displayed in the window.  The mode line contains information about the
 buffer, such as its name, associated file, depth of recursive editing,
-and major and minor modes.  A window can also have a @dfn{header
-line}, which is much like the mode line but appears at the top of the
-window.
+and major and minor modes.  A window can also have a @dfn{header line}
+and a @dfn{tab line}, which are much like the mode line but they appear
+at the top of the window.
 
-  This section describes how to control the contents of the mode line
-and header line.  We include it in this chapter because much of the
-information displayed in the mode line relates to the enabled major and
-minor modes.
+  This section describes how to control the contents of the mode line,
+header line, and tab line.  We include it in this chapter because much
+of the information displayed in the mode line relates to the enabled
+major and minor modes.
 
 @menu
 * Base: Mode Line Basics.       Basic ideas of mode line control.
@@ -2091,6 +2091,7 @@ minor modes.
 * %-Constructs::                Putting information into a mode line.
 * Properties in Mode::          Using text properties in the mode line.
 * Header Lines::                Like a mode line, but at the top.
+* Tab Lines::                   A line that is above the header line.
 * Emulating Mode Line::         Formatting text as the mode line would.
 @end menu
 
@@ -2101,11 +2102,13 @@ minor modes.
 variable @code{mode-line-format} (@pxref{Mode Line Top}).  This variable
 holds a @dfn{mode line construct}: a template that controls what is
 displayed on the buffer's mode line.  The value of
-@code{header-line-format} specifies the buffer's header line in the same
-way.  All windows for the same buffer use the same
-@code{mode-line-format} and @code{header-line-format} unless a
-@code{mode-line-format} or @code{header-line-format} parameter has been
-specified for that window (@pxref{Window Parameters}).
+@code{header-line-format} and @code{tab-line-format} specifies the
+buffer's header line and tab line in the same way.  All windows for the
+same buffer use the same @code{mode-line-format},
+@code{header-line-format}, and @code{tab-line-format} unless a
+@code{mode-line-format}, @code{header-line-format}, or
+@code{tab-line-format} parameter has been specified for that window
+(@pxref{Window Parameters}).
 
   For efficiency, Emacs does not continuously recompute each window's
 mode line and header line.  It does so when circumstances appear to call
@@ -2167,8 +2170,8 @@ buffers.
 @dfn{mode line construct}, made up of lists, strings, symbols, and
 numbers kept in buffer-local variables.  Each data type has a specific
 meaning for the mode line appearance, as described below.  The same data
-structure is used for constructing frame titles (@pxref{Frame Titles})
-and header lines (@pxref{Header Lines}).
+structure is used for constructing frame titles (@pxref{Frame Titles}),
+header lines (@pxref{Header Lines}), and tab lines (@pxref{Tab Lines}).
 
   A mode line construct may be as simple as a fixed string of text,
 but it usually specifies how to combine fixed strings with variables'
@@ -2816,6 +2819,31 @@ window that is two lines tall cannot display both a mode line and a
 header line at once; if it has a mode line, then it does not display a
 header line.
 
+@node Tab Lines
+@subsection Window Tab Lines
+@cindex tab line (of a window)
+@cindex window tab line
+
+  A window can have a @dfn{tab line} at the top.  If both the tab line
+and header line are visible, the tab line appears above the header line.
+The tab line feature is controlled like the mode line feature, except
+that it's controlled by @code{tab-line-format}.  Unlike the mode line,
+the tab line is only expected to be used to display a list of tabs
+(@pxref{Tab Line,,, emacs, The GNU Emacs Manual}) or the window
+tool bar (@pxref{Window Tool Bar,,, emacs, The GNU Emacs Manual}):
+
+@defvar tab-line-format
+This variable, local in every buffer, specifies how to display the tab
+line, for windows displaying the buffer.  The format of the value is the
+same as for @code{mode-line-format} (@pxref{Mode Line Data}).  It is
+normally @code{nil}, so that ordinary buffers have no tab line.
+@end defvar
+
+@defun window-tab-line-height &optional window
+This function returns the height in pixels of @var{window}'s tab line.
+@var{window} must be a live window, and defaults to the selected window.
+@end defun
+
 @node Emulating Mode Line
 @subsection Emulating Mode Line Formatting