In this walk-through, I will describe each new function as we come to it, sometimes in detail and sometimes briefly. If you are interested, you can get the full documentation of any Emacs Lisp function at any time by typing C-h f and then the name of the function (and then <RET>). Similarly, you can get the full documentation for a variable by typing C-h v and then the name of the variable (and then <RET>).
describe-function will tell you the location of the
Put point into the name of the file that contains the function and
press the <RET> key. In this case, <RET> means
push-button rather than “return” or “enter”. Emacs will take
you directly to the function definition.
More generally, if you want to see a function in its original source
file, you can use the
xref-find-definitions function to jump to
xref-find-definitions works with a wide variety of
languages, not just Lisp, and C, and it works with non-programming
text as well. For example,
xref-find-definitions will jump to
the various nodes in the Texinfo source file of this document
(provided that you've run the etags utility to record all
the nodes in the manuals that come with Emacs; see Create tags Table).
To use the
xref-find-definitions command, type M-.
(i.e., press the period key while holding down the <META> key, or
else type the <ESC> key and then type the period key), and then,
at the prompt, type in the name of the function whose source code you
want to see, such as
mark-whole-buffer, and then type
<RET>. (If the command doesn't prompt, invoke it with an
argument: C-u M-.; see Interactive Options.) Emacs will
switch buffers and display the source code for the function on your
screen1. To switch back to your current buffer, type M-, or
C-x b <RET>. (On some keyboards, the <META> key is
Incidentally, the files that contain Lisp code are conventionally called libraries. The metaphor is derived from that of a specialized library, such as a law library or an engineering library, rather than a general library. Each library, or file, contains functions that relate to a particular topic or activity, such as abbrev.el for handling abbreviations and other typing shortcuts, and help.el for help. (Sometimes several libraries provide code for a single activity, as the various rmail... files provide code for reading electronic mail.) In The GNU Emacs Manual, you will see sentences such as “The C-h p command lets you search the standard Emacs Lisp libraries by topic keywords.”
 If instead of showing the source code for a Lisp function, Emacs asks you which tags table to visit, invoke M-. from a buffer whose major mode is Emacs Lisp or Lisp Interaction.