Menus
*****

Format of Menus
===============

A menu is described using a menu description, which is a list of menu items, keyword-value pairs, strings, and submenus.  The menu description specifies which items are present in the menu, what function each item invokes, and whether the item is selectable or not.  Pop-up menus are directly described with a menu description, while menubars are described slightly differently (see below).

The first element of a menu must be a string, which is the name of the menu.  This is the string that will be displayed in the parent menu or menubar, if any.  This string is not displayed in the menu itself, except in the case of the top level pop-up menu, where there is no parent.  In this case, the string will be displayed at the top of the menu if popup-menu-titles is non-nil.

Immediately following the first element there may optionally be up to four keyword-value pairs, as follows:

:included FORM
     This can be used to control the visibility of a menu.  The form is evaluated and the menu will be omitted if the result is nil.

:config SYMBOL
     This is an efficient shorthand for :included (memq SYMBOL menubar-configuration).  See the variable menubar-configuration.

:filter FUNCTION
     A menu filter is used to sensitize or incrementally create a submenu only when it is selected by the user and not every time the menubar is activated.  The filter function is passed the list of menu items in the submenu and must return a list of menu items to be used for the menu. It is called only when the menu is about to be displayed, so other menus may already be displayed.  Vile and terrible things will happen if a menu filter function changes the current buffer, window, or frame.  It also should not raise, lower, or iconify any frames.  Basically, the filter function should have no side-effects.

:accelerator KEY
     A menu accelerator is a keystroke which can be pressed while the menu is visible which will immediately activate the item.  KEY must be a char or the symbol name of a key.  See Menu Accelerators.

The rest of the menu consists of elements as follows:

  * A menu item, which is a vector in the following form:

          [ NAME CALLBACK :KEYWORD VALUE :KEYWORD VALUE ... ]

     NAME is a string, the name of the menu item; it is the string to display on the menu.  It is filtered through the resource database, so it is possible for resources to override what string is actually displayed.

     CALLBACK is a form that will be invoked when the menu item is selected.  If the callback of a menu item is a symbol, then it must name a command.  It will be invoked with call-interactively.  If it is a list, then it is evaluated with eval.

     The valid keywords and their meanings are described below.

     Note that for compatibility purposes, the form

          [ NAME CALLBACK ACTIVE-P ]

     is also accepted and is equivalent to

          [ NAME CALLBACK :active ACTIVE-P ]

     and the form

          [ NAME CALLBACK ACTIVE-P SUFFIX]

     is accepted and is equivalent to

          [ NAME CALLBACK :active ACTIVE-P :suffix SUFFIX]

     However, these older forms are deprecated and should generally not be used.

  * If an element of a menu is a string, then that string will be presented in the menu as unselectable text.

  * If an element of a menu is a string consisting solely of hyphens, then that item will be presented as a solid horizontal line.

  * If an element of a menu is a string beginning with --:, then a particular sort of horizontal line will be displayed, as follows:

     "--:singleLine"
          A solid horizontal line.  This is equivalent to a string consisting solely of hyphens.

     "--:doubleLine"
          A solid double horizontal line.

     "--:singleDashedLine"
          A dashed horizontal line.

     "--:doubleDashedLine"
          A dashed double horizontal line.

     "--:noLine"
          No line (but a small space is left).

     "--:shadowEtchedIn"
          A solid horizontal line with a 3-d recessed appearance.

     "--:shadowEtchedOut"
          A solid horizontal line with a 3-d pushed-out appearance.

     "--:shadowDoubleEtchedIn"
          A solid double horizontal line with a 3-d recessed appearance.

     "--:shadowDoubleEtchedOut"
          A solid double horizontal line with a 3-d pushed-out appearance.

     "--:shadowEtchedInDash"
          A dashed horizontal line with a 3-d recessed appearance.

     "--:shadowEtchedOutDash"
          A dashed horizontal line with a 3-d pushed-out appearance.

     "--:shadowDoubleEtchedInDash"
          A dashed double horizontal line with a 3-d recessed appearance.

     "--:shadowDoubleEtchedOutDash"
          A dashed double horizontal line with a 3-d pushed-out appearance.

  * If an element of a menu is a list, it is treated as a submenu.  The name of that submenu (the first element in the list) will be used as the name of the item representing this menu on the parent.

The possible keywords are as follows:

:active FORM
     FORM will be evaluated when the menu that this item is a part of is about to be displayed, and the item will be selectable only if the result is non-nil.  If the item is unselectable, it will usually be displayed grayed-out to indicate this.

:suffix STRING
     The string is appended to the displayed name.  This provides a convenient way of adding the name of a command's ``argument'' to the menu, like Kill Buffer NAME.

:keys STRING
     Normally, the keyboard equivalents of commands in menus are displayed when the ``callback'' is a symbol.  This can be used to specify keys for more complex menu items.  It is passed through substitute-command-keys first.

:style STYLE
     Specifies what kind of object this menu item is.  STYLE be one of the symbols

     nil
          A normal menu item.

     toggle
          A toggle button.

     radio
          A radio button.

     button
          A menubar button.

     The only difference between toggle and radio buttons is how they are displayed.  But for consistency, a toggle button should be used when there is one option whose value can be turned on or off, and radio buttons should be used when there is a set of mutually exclusive options. When using a group of radio buttons, you should arrange for no more than one to be marked as selected at a time.

:selected FORM
     Meaningful only when STYLE is toggle, radio or button.  This specifies whether the button will be in the selected or unselected state.  FORM is evaluated, as for :active.

:included FORM
     This can be used to control the visibility of a menu item.  The form is evaluated and the menu item is only displayed if the result is non-nil.  Note that this is different from :active: If :active evaluates to nil, the item will be displayed grayed out, while if :included evaluates to nil, the item will be omitted entirely.

:config SYMBOL
     This is an efficient shorthand for :included (memq SYMBOL menubar-configuration).  See the variable menubar-configuration.

:accelerator KEY
     A menu accelerator is a keystroke which can be pressed while the menu is visible which will immediately activate the item.  KEY must be a char or the symbol name of a key.  See Menu Accelerators.

 -- Variable: menubar-configuration
     This variable holds a list of symbols, against which the value of the :config tag for each menubar item will be compared.  If a menubar item has a :config tag, then it is omitted from the menubar if that tag is not a member of the menubar-configuration list.

For example:

      ("File"
       :filter file-menu-filter	; file-menu-filter is a function that takes
     				; one argument (a list of menu items) and
     				; returns a list of menu items
       [ "Save As..."    write-file  t ]
       [ "Revert Buffer" revert-buffer (buffer-modified-p) ]
       [ "Read Only"     toggle-read-only :style toggle :selected buffer-read-only ]
       )

Format of the Menubar
=====================

A menubar is a list of menus, menu items, and strings.  The format is similar to that of a menu, except:

  * The first item need not be a string, and is not treated specially.

  * A string consisting solely of hyphens is not treated specially.

  * If an element of a menubar is nil, then it is used to represent the division between the set of menubar items which are flush-left and those which are flush-right.  (Note: this isn't completely implemented yet.)

Menubar
=======

 -- Variable: current-menubar
     This variable holds the description of the current menubar.  This may be buffer-local.  When the menubar is changed, the function set-menubar-dirty-flag has to be called in order for the menubar to be updated on the screen.

 -- Constant: default-menubar
     This variable holds the menubar description of the menubar that is visible at startup.  This is the value that current-menubar has at startup.

 -- Function: set-menubar-dirty-flag
     This function tells XEmacs that the menubar widget has to be updated. Changes to the menubar will generally not be visible until this function is called.

The following convenience functions are provided for setting the menubar.  They are equivalent to doing the appropriate action to change current-menubar, and then calling set-menubar-dirty-flag. Note that these functions copy their argument using copy-sequence.

 -- Function: set-menubar menubar
     This function sets the default menubar to be MENUBAR (see Menu Format).  This is the menubar that will be visible in buffers that have not defined their own, buffer-local menubar.

 -- Function: set-buffer-menubar menubar
     This function sets the buffer-local menubar to be MENUBAR.  This does not change the menubar in any buffers other than the current one.

Miscellaneous:

 -- Variable: menubar-show-keybindings
     If true, the menubar will display keyboard equivalents.  If false, only the command names will be displayed.

 -- Variable: activate-menubar-hook
     Function or functions called before a menubar menu is pulled down. These functions are called with no arguments, and should interrogate and modify the value of current-menubar as desired.

     The functions on this hook are invoked after the mouse goes down, but before the menu is mapped, and may be used to activate, deactivate, add, or delete items from the menus.  However, using a filter (with the :filter keyword in a menu description) is generally a more efficient way of accomplishing the same thing, because the filter is invoked only when the actual menu goes down.  With a complex menu, there can be a quite noticeable and sometimes aggravating delay if all menu modification is implemented using the activate-menubar-hook. See above.

     These functions may return the symbol t to assert that they have made no changes to the menubar.  If any other value is returned, the menubar is recomputed.  If t is returned but the menubar has been changed, then the changes may not show up right away.  Returning nil when the menubar has not changed is not so bad; more computation will be done, but redisplay of the menubar will still be performed optimally.

 -- Variable: menu-no-selection-hook
     Function or functions to call when a menu or dialog box is dismissed without a selection having been made.

Modifying Menus
===============

The following functions are provided to modify the menubar of one of its submenus.  Note that these functions modify the menu in-place, rather than copying it and making a new menu.

Some of these functions take a menu path, which is a list of strings identifying the menu to be modified.  For example, ("File") names the top-level ``File'' menu.  ("File" "Foo") names a hypothetical submenu of ``File''.

Others take a menu item path, which is similar to a menu path but also specifies a particular item to be modified.  For example, ("File" "Save") means the menu item called ``Save'' under the top-level ``File'' menu.  ("Menu" "Foo" "Item") means the menu item called ``Item'' under the ``Foo'' submenu of ``Menu''.

 -- Function: add-submenu menu-path submenu &optional before
     This function adds a menu to the menubar or one of its submenus.  If the named menu exists already, it is changed.

     MENU-PATH identifies the menu under which the new menu should be inserted.  If MENU-PATH is nil, then the menu will be added to the menubar itself.

     SUBMENU is the new menu to add (see Menu Format).

     BEFORE, if provided, is the name of a menu before which this menu should be added, if this menu is not on its parent already.  If the menu is already present, it will not be moved.

 -- Function: add-menu-button menu-path menu-leaf &optional before
     This function adds a menu item to some menu, creating the menu first if necessary.  If the named item exists already, it is changed.

     MENU-PATH identifies the menu under which the new menu item should be inserted.

     MENU-LEAF is a menubar leaf node (see Menu Format).

     BEFORE, if provided, is the name of a menu before which this item should be added, if this item is not on the menu already.  If the item is already present, it will not be moved.

 -- Function: delete-menu-item menu-item-path
     This function removes the menu item specified by MENU-ITEM-PATH from the menu hierarchy.

 -- Function: enable-menu-item menu-item-path
     This function makes the menu item specified by MENU-ITEM-PATH be selectable.

 -- Function: disable-menu-item menu-item-path
     This function makes the menu item specified by MENU-ITEM-PATH be unselectable.

 -- Function: relabel-menu-item menu-item-path new-name
     This function changes the string of the menu item specified by MENU-ITEM-PATH.  NEW-NAME is the string that the menu item will be printed as from now on.

The following function can be used to search for a particular item in a menubar specification, given a path to the item.

 -- Function: find-menu-item menubar menu-item-path &optional parent
     This function searches MENUBAR for the item given by MENU-ITEM-PATH starting from PARENT (nil means start at the top of MENUBAR).  This function returns (ITEM . PARENT), where PARENT is the immediate parent of the item found (a menu description), and ITEM is either a vector, list, or string, depending on the nature of the menu item.

     This function signals an error if the item is not found.

The following deprecated functions are also documented, so that existing code can be understood.  You should not use these functions in new code.

 -- Function: add-menu menu-path menu-name menu-items &optional before
     This function adds a menu to the menubar or one of its submenus.  If the named menu exists already, it is changed.  This is obsolete; use add-submenu instead.

     MENU-PATH identifies the menu under which the new menu should be inserted.  If MENU-PATH is nil, then the menu will be added to the menubar itself.

     MENU-NAME is the string naming the menu to be added; MENU-ITEMS is a list of menu items, strings, and submenus.  These two arguments are the same as the first and following elements of a menu description (see Menu Format).

     BEFORE, if provided, is the name of a menu before which this menu should be added, if this menu is not on its parent already.  If the menu is already present, it will not be moved.

 -- Function: add-menu-item menu-path item-name function enabled-p &optional before
     This function adds a menu item to some menu, creating the menu first if necessary.  If the named item exists already, it is changed.  This is obsolete; use add-menu-button instead.

     MENU-PATH identifies the menu under which the new menu item should be inserted. ITEM-NAME, FUNCTION, and ENABLED-P are the first, second, and third elements of a menu item vector (see Menu Format).

     BEFORE, if provided, is the name of a menu item before which this item should be added, if this item is not on the menu already.  If the item is already present, it will not be moved.

Menu Filters
============

The following filter functions are provided for use in default-menubar.  You may want to use them in your own menubar description.

 -- Function: file-menu-filter menu-items
     This function changes the arguments and sensitivity of these File menu items:

     Delete Buffer
          Has the name of the current buffer appended to it.

     Print Buffer
          Has the name of the current buffer appended to it.

     Pretty-Print Buffer
          Has the name of the current buffer appended to it.

     Save Buffer
          Has the name of the current buffer appended to it, and is sensitive only when the current buffer is modified.

     Revert Buffer
          Has the name of the current buffer appended to it, and is sensitive only when the current buffer has a file.

     Delete Frame
          Sensitive only when there is more than one visible frame.

 -- Function: edit-menu-filter menu-items
     This function changes the arguments and sensitivity of these Edit menu items:

     Cut
          Sensitive only when XEmacs owns the primary X Selection (if zmacs-regions is t, this is equivalent to saying that there is a region selected).

     Copy
          Sensitive only when XEmacs owns the primary X Selection.

     Clear
          Sensitive only when XEmacs owns the primary X Selection.

     Paste
          Sensitive only when there is an owner for the X Clipboard Selection.

     Undo
          Sensitive only when there is undo information.  While in the midst of an undo, this is changed to Undo More.

 -- Function: buffers-menu-filter menu-items
     This function sets up the Buffers menu.  See Buffers Menu for more information.

Pop-Up Menus
============

 -- Function: popup-menu menu-desc
     This function pops up a menu specified by MENU-DESC, which is a menu description (see Menu Format).  The menu is displayed at the current mouse position.

 -- Function: popup-menu-up-p
     This function returns t if a pop-up menu is up, nil otherwise.

 -- Variable: popup-menu-titles
     If true (the default), pop-up menus will have title bars at the top.

Some machinery is provided that attempts to provide a higher-level mechanism onto pop-up menus.  This only works if you do not redefine the binding for button3.

 -- Command: popup-mode-menu
     This function pops up a menu of global and mode-specific commands.  The menu is computed by combining global-popup-menu and mode-popup-menu.  This is the default binding for button3. You should generally not change this binding.

 -- Variable: global-popup-menu
     This holds the global popup menu.  This is present in all modes. (This is nil by default.)

 -- Variable: mode-popup-menu
     The mode-specific popup menu.  Automatically buffer local. This is appended to the default items in global-popup-menu.

 -- Constant: default-popup-menu
     This holds the default value of mode-popup-menu.

 -- Variable: activate-popup-menu-hook
     Function or functions run before a mode-specific popup menu is made visible.  These functions are called with no arguments, and should interrogate and modify the value of global-popup-menu or mode-popup-menu as desired.  Note: this hook is only run if you use popup-mode-menu for activating the global and mode-specific commands; if you have your own binding for button3, this hook won't be run.

The following convenience functions are provided for displaying pop-up menus.

 -- Function: popup-buffer-menu event
     This function pops up a copy of the Buffers menu (from the menubar) where the mouse is clicked.

 -- Function: popup-menubar-menu event
     This function pops up a copy of menu that also appears in the menubar.

Menu Accelerators
=================

Menu accelerators are keyboard shortcuts for accessing the menubar. Accelerator keys can be specified for menus as well as for menu items.  An accelerator key for a menu is used to activate that menu when it appears as a submenu of another menu.  An accelerator key for a menu item is used to activate that item.

Creating Menu Accelerators
--------------------------

Menu accelerators are specified as part of the menubar format using the :accelerator tag to specify a key or by placing "%_" in the menu or menu item name prior to the letter which is to be used as the accelerator key.  The advantage of the second method is that the menu rendering code then knows to draw an underline under that character, which is the canonical way of indicating an accelerator key to a user.

For example, the command

     (add-submenu nil '("%_Test"
     		   ["One" (insert "1") :accelerator ?1 :active t]
     		   ["%_Two" (insert "2") t]
     		   ["%_3" (insert "3") t]))

will add a new menu to the top level menubar.  The new menu can be reached by pressing "t" while the top level menubar is active.  When the menu is active, pressing "1" will activate the first item and insert the character "1" into the buffer.  Pressing "2" will activate the second item and insert the character "2" into the buffer.  Pressing "3" will activate the third item and insert the character "3" into the buffer.

It is possible to activate the top level menubar itself using accelerator keys. See Menu Accelerator Functions.

Keyboard Menu Traversal
-----------------------

In addition to immediately activating a menu or menu item, the keyboard can be used to traverse the menus without activating items.  The keyboard arrow keys, the return key and the escape key are defined to traverse the menus in a way that should be familiar to users of any of a certain family of popular PC operating systems.

This behaviour can be changed by modifying the bindings in menu-accelerator-map.  At this point, the online help is your best bet for more information about how to modify the menu traversal keys.

Menu Accelerator Functions
--------------------------

 -- Function: accelerate-menu
     Make the menubar immediately active and place the cursor on the left most entry in the top level menu.  Menu items can be selected as usual.

 -- Variable: menu-accelerator-enabled
     Whether menu accelerator keys can cause the menubar to become active.

     If menu-force or menu-fallback, then menu accelerator keys can be used to activate the top level menu.  Once the menubar becomes active, the accelerator keys can be used regardless of the value of this variable.

     menu-force is used to indicate that the menu accelerator key takes precedence over bindings in the current keymap(s).  menu-fallback means that bindings in the current keymap take precedence over menu accelerator keys. Thus a top level menu with an accelerator of "T" would be activated on a keypress of Meta-t if MENU-ACCELERATOR-ENABLED is menu-force. However, if MENU-ACCELERATOR-ENABLED is menu-fallback, then Meta-t will not activate the menubar and will instead run the function transpose-words, to which it is normally bound.

     The default value is nil.

     See also MENU-ACCELERATOR-MODIFIERS and MENU-ACCELERATOR-PREFIX.

 -- Variable: menu-accelerator-map
     Keymap consulted to determine the commands to run in response to keypresses occurring while the menubar is active.  See Keyboard Menu Traversal.

 -- Variable: menu-accelerator-modifiers
     A list of modifier keys which must be pressed in addition to a valid menu accelerator in order for the top level menu to be activated in response to a keystroke.  The default value of (meta) mirrors the useage of the alt key as a menu accelerator in popular PC operating systems.

     The modifier keys in MENU-ACCELERATOR-MODIFIERS must match exactly the modifiers present in the keypress.  The only exception is that the shift modifier is accepted in conjunction with alphabetic keys even if it is not a menu accelerator modifier.

     See also MENU-ACCELERATOR-ENABLED and MENU-ACCELERATOR-PREFIX.

 -- Variable: menu-accelerator-prefix
     Prefix key(s) that must be typed before menu accelerators will be activated. Must be a valid key descriptor.

     The default value is nil.

     (setq menu-accelerator-prefix ?\C-x)
     (setq menu-accelerator-modifiers '(meta control))
     (setq menu-accelerator-enabled 'menu-force)
     (add-submenu nil '("%_Test"
     		   ["One" (insert "1") :accelerator ?1 :active t]
     		   ["%_Two" (insert "2") t]
     		   ["%_3" (insert "3") t]))

will add the menu "Test" to the top level menubar.  Pressing C-x followed by C-M-T will activate the menubar and display the "Test" menu.  Pressing C-M-T by itself will not activate the menubar.  Neither will pressing C-x followed by anything else.

Buffers Menu
============

The following options control how the Buffers menu is displayed. This is a list of all (or a subset of) the buffers currently in existence, and is updated dynamically.

 -- User Option: buffers-menu-max-size
     This user option holds the maximum number of entries which may appear on the Buffers menu.  If this is 10, then only the ten most-recently-selected buffers will be shown.  If this is nil, then all buffers will be shown.  Setting this to a large number or nil will slow down menu responsiveness.

 -- Function: format-buffers-menu-line buffer
     This function returns a string to represent BUFFER in the Buffers menu.  nil means the buffer shouldn't be listed. You can redefine this.

 -- User Option: complex-buffers-menu-p
     If true, the Buffers menu will contain several commands, as submenus of each buffer line.  If this is false, then there will be only one command: select that buffer.

 -- User Option: buffers-menu-switch-to-buffer-function
     This user option holds the function to call to select a buffer from the Buffers menu.  switch-to-buffer is a good choice, as is pop-to-buffer.