Emacs provides a variety of built-in help functions, all accessible to the user as subcommands of the prefix C-h. For more information about them, see Help in The GNU Emacs Manual. Here we describe some program-level interfaces to the same information.
This function finds all meaningful symbols whose names contain a match for the apropos pattern pattern. An apropos pattern is either a word to match, a space-separated list of words of which at least two must match, or a regular expression (if any special regular expression characters occur). A symbol is meaningful if it has a definition as a function, variable, or face, or has properties.
The function returns a list of elements that look like this:
(symbol score function-doc variable-doc plist-doc widget-doc face-doc group-doc)
Here, score is an integer measure of how important the symbol
seems to be as a match. Each of the remaining elements is a
documentation string, or nil, for symbol as a function,
variable, etc.
It also displays the symbols in a buffer named *Apropos*, each with a one-line description taken from the beginning of its documentation string.
If do-all is non-nil, or if the user option
apropos-do-all is non-nil, then apropos also
shows key bindings for the functions that are found; it also shows
all interned symbols, not just meaningful ones (and it lists
them in the return value as well).
The value of this variable is a local keymap for characters following the Help key, C-h.
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:
(keymap-set global-map (key-description (string help-char)) 'help-command) (fset 'help-command help-map)
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.
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.
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, read-char-choice,
read-char, read-char-from-minibuffer, or
y-or-n-p 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 Definition of minibuffer-help-form).
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.
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.
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.
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.
This variable holds the name of the directory in which Emacs finds certain documentation and text files that come with Emacs.
This function returns the name of the help buffer, which is normally *Help*; if such a buffer does not exist, it is first created.
This macro evaluates body like with-output-to-temp-buffer
(see Temporary Displays), inserting any output produced by its
forms into a buffer specified by buffer-or-name, which can be a
buffer or the name of a buffer. (Frequently, buffer-or-name is
the value returned by the function help-buffer.) This macro
puts the specified buffer into Help mode and displays a message
telling the user how to quit and scroll the help window. It selects
the help window if the current value of the user option
help-window-select has been set accordingly. It returns the
last value in body.
This function updates the cross reference data in the *Help*
buffer, which is used to regenerate the help information when the user
clicks on the ‘Back’ or ‘Forward’ buttons. Most commands
that use the *Help* buffer should invoke this function before
clearing the buffer. The item argument should have the form
(function . args), where function is a function
to call, with argument list args, to regenerate the help buffer.
The interactive-p argument is non-nil if the calling
command was invoked interactively; in that case, the stack of items
for the *Help* buffer’s ‘Back’ buttons is cleared.
See describe-symbols example, for an example of using
help-buffer, with-help-window, and
help-setup-xref.
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.
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.