2.3 Keys and Commands
This manual is full of passages that tell you what particular keys do.
But Emacs does not assign meanings to keys directly. Instead, Emacs
assigns meanings to "functions", and then gives keys their meanings by
"binding" them to functions.
A function is a Lisp object that can be executed as a program.
Usually it is a Lisp symbol that has been given a function definition;
every symbol has a name, usually made of a few English words separated
by dashes, such as `next-line' or `forward-word'. It also has a
"definition", which is a Lisp program. Only some functions can be the
bindings of keys; these are functions whose definitions use
`interactive' to specify how to call them interactively. Such
functions are called "commands", and their names are "command names".
More information on this subject will appear in the XEmacs Lisp
The bindings between keys and functions are recorded in various
tables called "keymaps". Note: Key Bindings, for more information on
key sequences you can bind commands to. Note: Keymaps, for
information on creating keymaps.
When we say "`C-n' moves down vertically one line" we are glossing
over a distinction that is irrelevant in ordinary use but is vital in
understanding how to customize Emacs. The function `next-line' is
programmed to move down vertically. `C-n' has this effect because it
is bound to that function. If you rebind `C-n' to the function
`forward-word' then `C-n' will move forward by words instead.
Rebinding keys is a common method of customization.
The rest of this manual usually ignores this subtlety to keep things
simple. To give the customizer the information needed, we often state
the name of the command that really does the work in parentheses after
mentioning the key that runs it. For example, we will say that "The
command `C-n' (`next-line') moves point vertically down," meaning that
`next-line' is a command that moves vertically down and `C-n' is a key
that is standardly bound to it.
While we are on the subject of information for customization only,
it's a good time to tell you about "variables". Often the description
of a command will say, "To change this, set the variable `mumble-foo'."
A variable is a name used to remember a value. Most of the variables
documented in this manual exist just to facilitate customization: some
command or other part of Emacs uses the variable and behaves
differently depending on its setting. Until you are interested in
customizing, you can ignore the information about variables. When you
are ready to be interested, read the basic information on variables, and
then the information on individual variables will make sense. Note:
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