12.3 Help by Command or Variable Name

C-h x command RET (describe-command) displays the documentation of the named command, in a window. For example,

C-h x auto-fill-mode RET

displays the documentation of auto-fill-mode. This is how you would get the documentation of a command that is not bound to any key (one which you would normally run using M-x).

C-h f function RET (describe-function) displays the documentation of Lisp function. This command is intended for Lisp functions that you use in a Lisp program. For example, if you have just written the expression (make-vector len) and want to check that you are using make-vector properly, type C-h f make-vector RET. Additionally, since all commands are Lisp functions, you can also use this command to view the documentation of any command.

If you type C-h f RET, it describes the function called by the innermost Lisp expression in the buffer around point, provided that function name is a valid, defined Lisp function. (That name appears as the default while you enter the argument.) For example, if point is located following the text ‘(make-vector (car x)’, the innermost list containing point is the one that starts with ‘(make-vector’, so C-h f RET describes the function make-vector.

C-h f is also useful just to verify that you spelled a function name correctly. If the minibuffer prompt for C-h f shows the function name from the buffer as the default, it means that name is defined as a Lisp function. Type C-g to cancel the C-h f command if you don’t really want to view the documentation.

The function’s documentation displayed by describe-function includes more than just the documentation string and the signature of the function. It also shows auxiliary information such as its type, the file where it was defined, whether it has been declared obsolete, and yet further information is often reachable by clicking or typing RET on emphasized parts of the text.

The function type, if known, is expressed with a function type specifier (see Type Specifiers in The Emacs Lisp Reference Manual), it will be specified if the type was manually declared by a Lisp program or inferred by the compiler. Note that function type inference works only when native compilation is enabled (see native compilation in The Emacs Lisp Reference Manual).

If you request help for an autoloaded function whose autoload form (see Autoload in The Emacs Lisp Reference Manual) doesn’t provide a doc string, the *Help* buffer won’t have any doc string to display. In that case, if help-enable-symbol-autoload is non-nil, Emacs will try to load the file in which the function is defined to see whether there’s a doc string there.

You can get an overview of functions relevant for a particular topic by using the M-x shortdoc command. This will prompt you for an area of interest, e.g., string, and pop you to a buffer where many of the functions relevant for handling strings are listed.

You can also request that documentation of functions and commands shown in *Help* buffers popped by C-h f includes examples of their use. To that end, add the following to your initialization file (see The Emacs Initialization File):

(add-hook 'help-fns-describe-function-functions
          #'shortdoc-help-fns-examples-function)

C-h v (describe-variable) is like C-h f but describes Lisp variables instead of Lisp functions. Its default is the Lisp symbol around or before point, if that is the name of a defined Lisp variable. See Variables.

Help buffers that describe Emacs variables and functions normally have hyperlinks to the corresponding source code, if you have the source files installed (see Hyperlinking and Web Navigation Features).

To find a command’s documentation in a manual, use C-h F (Info-goto-emacs-command-node). This knows about various manuals, not just the Emacs manual, and finds the right one.

C-h o (describe-symbol) is like C-h f and C-h v, but it describes any symbol, be it a function, a variable, or a face. If the symbol has more than one definition, like it has both definition as a function and as a variable, this command will show the documentation of all of them, one after the other.

C-h 4 s (help-find-source) switch to a buffer visiting the source definition of what is being described in the help buffer.

If the completions-detailed user option is non-nil, some commands provide details about the possible values when displaying completions. For instance, C-h o TAB will then include the first line of the doc string, and will also say whether each symbol is a function or a variable (and so on). Which details are included varies depending on the command used.