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 section `Help' in The GNU Emacs Manual. Here we describe some program-level interfaces to the same information.
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)
help-map. It is defined in `help.el' as
follows:
(define-key global-map "\C-h" 'help-command) (fset 'help-command help-map)
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 section Access to Documentation Strings.
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.
help-char.
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 (see section Minibuffer Miscellany).
describe-prefix-bindings.
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.
describe-bindings.
nil.
This can be customized by changing the map Helper-help-map.
exec-directory was used for this.
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.
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.
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