You are reading about GNU Emacs, the GNU incarnation of the advanced, selfdocumenting, customizable, extensible editor Emacs. (The ‘G’ in ‘GNU’ is not
We call Emacs advanced because it can do much more than simple insertion and deletion
of text. It can control subprocesses, indent programs automatically, show multiple files at
once, and more. Emacs editing commands operate in terms of characters, words, lines, sentences, paragraphs, and pages, as well as expressions and comments in various programminglanguages.
Self-documenting means that at any time you can use special commands, known as help
commands, to find out what your options are, or to find out what any command does, or
to find all the commands that pertain to a given topic. See Chapter 7 [Help], page 37.
Customizable means that you can easily alter the behavior of Emacs commands in simple
ways. For instance, if you use a programming language in which comments start with ‘<**’
and end with ‘**>’, you can tell the Emacs comment manipulation commands to use those
strings (see Section 23.5 [Comments], page 243). To take another example, you can rebind
the basic cursor motion commands (up, down, left and right) to any keys on the keyboard
that you find comfortable. See Chapter 33 [Customization], page 404.
Extensible means that you can go beyond simple customization and create entirely new
commands. New commands are simply programs written in the Lisp language, which are run
by Emacs’s own Lisp interpreter. Existing commands can even be redefined in the middle
of an editing session, without having to restart Emacs. Most of the editing commands in
Emacs are written in Lisp; the few exceptions could have been written in Lisp but use C
instead for efficiency. Writing an extension is programming, but non-programmers can use
it afterwards. See Section “Preface” in An Introduction to Programming in Emacs Lisp, if
you want to learn Emacs Lisp programming.