GNU Info

(elisp)Help Functions

---

Prev: Describing Characters Up: Documentation

---

Enter node , (file) or (file)node

Help Functions
==============

   Emacs provides a variety of on-line help functions, all accessible to
the user as subcommands of the prefix `C-h'.  For more information
about them, see Note: Help.  Here we describe some
program-level interfaces to the same information.

 - Command: apropos regexp &optional do-all
     This function finds all symbols whose names contain a match for the
     regular expression REGEXP, and returns a list of them (Note:
     Regular Expressions).  It also displays the symbols in a buffer
     named `*Help*', each with a one-line description taken from the
     beginning of its documentation string.

     If DO-ALL is non-`nil', then `apropos' also shows key bindings for
     the functions that are found; it also shows all symbols, even
     those that are neither functions nor variables.

     In the first of the following examples, `apropos' finds all the
     symbols with names containing `exec'.  (We don't show here the
     output that results in the `*Help*' buffer.)

          (apropos "exec")
               => (Buffer-menu-execute command-execute exec-directory
              exec-path execute-extended-command execute-kbd-macro
              executing-kbd-macro executing-macro)

 - Variable: help-map
     The value of this variable is a local keymap for characters
     following the Help key, `C-h'.

 - Prefix Command: help-command
     This symbol is not a function; its function definition cell holds
     the keymap known as `help-map'.  It is defined in `help.el' as
     follows:

          (define-key global-map "\C-h" 'help-command)
          (fset 'help-command help-map)

 - Function: print-help-return-message &optional function
     This function builds a string that explains how to restore the
     previous state of the windows after a help command.  After
     building the message, it applies FUNCTION to it if FUNCTION is
     non-`nil'.  Otherwise it calls `message' to display it in the echo
     area.

     This function expects to be called inside a
     `with-output-to-temp-buffer' special form, and expects
     `standard-output' to have the value bound by that special form.
     For an example of its use, see the long example in Note: Accessing
     Documentation.

 - Variable: help-char
     The value of this variable is the help character--the character
     that Emacs recognizes as meaning Help.  By default, its value is
     8, which stands for `C-h'.  When Emacs reads this character, if
     `help-form' is a non-`nil' Lisp expression, it evaluates that
     expression, and displays the result in a window if it is a string.

     Usually the value of `help-form' is `nil'.  Then the help
     character has no special meaning at the level of command input, and
     it becomes part of a key sequence in the normal way.  The standard
     key binding of `C-h' is a prefix key for several general-purpose
     help features.

     The help character is special after prefix keys, too.  If it has no
     binding as a subcommand of the prefix key, it runs
     `describe-prefix-bindings', which displays a list of all the
     subcommands of the prefix key.

 - Variable: help-event-list
     The value of this variable is a list of event types that serve as
     alternative "help characters."  These events are handled just like
     the event specified by `help-char'.

 - Variable: help-form
     If this variable is non-`nil', its value is a form to evaluate
     whenever the character `help-char' is read.  If evaluating the form
     produces a string, that string is displayed.

     A command that calls `read-event' or `read-char' probably should
     bind `help-form' to a non-`nil' expression while it does input.
     (The time when you should not do this is when `C-h' has some other
     meaning.)  Evaluating this expression should result in a string
     that explains what the input is for and how to enter it properly.

     Entry to the minibuffer binds this variable to the value of
     `minibuffer-help-form' (Note: Minibuffer Misc).

 - Variable: prefix-help-command
     This variable holds a function to print help for a prefix key.  The
     function is called when the user types a prefix key followed by
     the help character, and the help character has no binding after
     that prefix.  The variable's default value is
     `describe-prefix-bindings'.

 - Function: describe-prefix-bindings
     This function calls `describe-bindings' to display a list of all
     the subcommands of the prefix key of the most recent key sequence.
     The prefix described consists of all but the last event of that
     key sequence.  (The last event is, presumably, the help character.)

   The following two functions are meant for modes that want to provide
help without relinquishing control, such as the "electric" modes.
Their names begin with `Helper' to distinguish them from the ordinary
help functions.

 - Command: Helper-describe-bindings
     This command pops up a window displaying a help buffer containing a
     listing of all of the key bindings from both the local and global
     keymaps.  It works by calling `describe-bindings'.

 - Command: Helper-help
     This command provides help for the current mode.  It prompts the
     user in the minibuffer with the message `Help (Type ? for further
     options)', and then provides assistance in finding out what the key
     bindings are, and what the mode is intended for.  It returns `nil'.

     This can be customized by changing the map `Helper-help-map'.

 - Variable: data-directory
     This variable holds the name of the directory in which Emacs finds
     certain documentation and text files that come with Emacs.  In
     older Emacs versions, `exec-directory' was used for this.

 - Macro: make-help-screen fname help-line help-text help-map
     This macro defines a help command named FNAME that acts like a
     prefix key that shows a list of the subcommands it offers.

     When invoked, FNAME displays HELP-TEXT in a window, then reads and
     executes a key sequence according to HELP-MAP.  The string
     HELP-TEXT should describe the bindings available in HELP-MAP.

     The command FNAME is defined to handle a few events itself, by
     scrolling the display of HELP-TEXT.  When FNAME reads one of those
     special events, it does the scrolling and then reads another
     event.  When it reads an event that is not one of those few, and
     which has a binding in HELP-MAP, it executes that key's binding and
     then returns.

     The argument HELP-LINE should be a single-line summary of the
     alternatives in HELP-MAP.  In the current version of Emacs, this
     argument is used only if you set the option `three-step-help' to
     `t'.

     This macro is used in the command `help-for-help' which is the
     binding of `C-h C-h'.

 - User Option: three-step-help
     If this variable is non-`nil', commands defined with
     `make-help-screen' display their HELP-LINE strings in the echo
     area at first, and display the longer HELP-TEXT strings only if
     the user types the help character again.