how Emacs interprets your keyboard and mouse input.
@end iftex
+@ifnottex
+@raisesections
+@end ifnottex
+
@node User Input, Keys, Screen, Top
@section Kinds of User Input
@cindex input with the keyboard
@cindex keyboard input
@cindex character set (keyboard)
-@cindex ASCII
+@cindex @acronym{ASCII}
@cindex C-
@cindex Control
@cindex control characters
- GNU Emacs uses an extension of the ASCII character set for keyboard
+ GNU Emacs uses an extension of the @acronym{ASCII} character set for keyboard
input; it also accepts non-character input events including function
keys and mouse button actions.
- ASCII consists of 128 character codes. Some of these codes are
+ @acronym{ASCII} consists of 128 character codes. Some of these codes are
assigned graphic symbols such as @samp{a} and @samp{=}; the rest are
control characters, such as @kbd{Control-a} (usually written @kbd{C-a}
for short). @kbd{C-a} gets its name from the fact that you type it by
holding down the @key{CTRL} key while pressing @kbd{a}.
- Some ASCII control characters have special names, and most terminals
+ Some @acronym{ASCII} control characters have special names, and most terminals
have special keys you can type them with: for example, @key{RET},
@key{TAB}, @key{DEL} and @key{ESC}. The space character is usually
referred to below as @key{SPC}, even though strictly speaking it is a
graphic character whose graphic happens to be blank. Some keyboards
have a key labeled ``linefeed'' which is an alias for @kbd{C-j}.
- Emacs extends the ASCII character set with thousands more printing
+ Emacs extends the @acronym{ASCII} character set with thousands more printing
characters (@pxref{International}), additional control characters, and a
few more modifiers that can be combined with any character.
- On ASCII terminals, there are only 32 possible control characters.
+ On @acronym{ASCII} terminals, there are only 32 possible control characters.
These are the control variants of letters and @samp{@@[]\^_}. In
addition, the shift key is meaningless with control characters:
@kbd{C-a} and @kbd{C-A} are the same character, and Emacs cannot
@cindex @key{ESC} replacing @key{META} key
Some terminals have a @key{META} key, and allow you to type Meta
characters by holding this key down. Thus, @kbd{Meta-a} is typed by
-holding down @key{META} and pressing @kbd{a}. The @key{META} key works
-much like the @key{SHIFT} key. Such a key is not always labeled
-@key{META}, however, as this function is often a special option for a key
-with some other primary purpose.@refill
+holding down @key{META} and pressing @kbd{a}. The @key{META} key
+works much like the @key{SHIFT} key. Such a key is not always labeled
+@key{META}, however, as this function is often a special option for a
+key with some other primary purpose. Sometimes it is labeled
+@key{ALT} or @key{EDIT}; on a Sun keyboard, it may have a diamond on
+it.
If there is no @key{META} key, you can still type Meta characters
-using two-character sequences starting with @key{ESC}. Thus, to enter
-@kbd{M-a}, you could type @kbd{@key{ESC} a}. To enter @kbd{C-M-a}, you
-would type @kbd{@key{ESC} C-a}. @key{ESC} is allowed on terminals with
-@key{META} keys, too, in case you have formed a habit of using it.
-
+using two-character sequences starting with @key{ESC}. Thus, you can
+enter @kbd{M-a} by typing @kbd{@key{ESC} a}. You can enter
+@kbd{C-M-a} by typing @kbd{@key{ESC} C-a}. Unlike @key{META}, which
+modifies other characters, @key{ESC} is a separate character. You
+don't hold down @key{ESC} while typing the next character; instead,
+you press it and release it, then you enter the next character.
+@key{ESC} is allowed on terminals with @key{META} keys, too, in case
+you have formed a habit of using it.
+
The X Window System provides several other modifier keys that can be
applied to any input character. These are called @key{SUPER},
@key{HYPER} and @key{ALT}. We write @samp{s-}, @samp{H-} and @samp{A-}
modifiers. But you can assign them meanings of your own by customizing
Emacs.
+ If your keyboard lacks one of these modifier keys, you can enter it
+using @kbd{C-x @@}: @kbd{C-x @@ h} adds the ``hyper'' flag to the next
+character, @kbd{C-x @@ s} adds the ``super'' flag, and @kbd{C-x @@ a}
+adds the ``alt'' flag. For instance, @kbd{C-x @@ h C-a} is a way to
+enter @kbd{Hyper-Control-a}. (Unfortunately there is no way to add
+two modifiers by using @kbd{C-x @@} twice for the same character,
+because the first one goes to work on the @kbd{C-x}.)
+
Keyboard input includes keyboard keys that are not characters at all:
for example function keys and arrow keys. Mouse buttons are also
outside the gamut of characters. You can modify these events with the
programming, but simply want to redefine the meaning of some characters
or non-character events, see @ref{Customization}.
- ASCII terminals cannot really send anything to the computer except
-ASCII characters. These terminals use a sequence of characters to
+ @acronym{ASCII} terminals cannot really send anything to the computer except
+@acronym{ASCII} characters. These terminals use a sequence of characters to
represent each function key. But that is invisible to the Emacs user,
because the keyboard input routines recognize these special sequences
and convert them to function key events before any other part of Emacs
@cindex key sequence
@cindex key
A @dfn{key sequence} (@dfn{key}, for short) is a sequence of input
-events that are meaningful as a unit---as ``a single command.''
-Some Emacs command sequences are just one character or one event; for
-example, just @kbd{C-f} is enough to move forward one character. But
-Emacs also has commands that take two or more events to invoke.
+events that are meaningful as a unit---as ``a single command.'' Some
+Emacs command sequences are just one character or one event; for
+example, just @kbd{C-f} is enough to move forward one character in the
+buffer. But Emacs also has commands that take two or more events to
+invoke.
@cindex complete key
@cindex prefix key
command bindings. A few of them are prefix keys. A prefix key combines
with the following input event to make a longer key sequence, which may
itself be complete or a prefix. For example, @kbd{C-x} is a prefix key,
-so @kbd{C-x} and the next input event combine to make a two-character
+so @kbd{C-x} and the next input event combine to make a two-event
key sequence. Most of these key sequences are complete keys, including
@kbd{C-x C-f} and @kbd{C-x b}. A few, such as @kbd{C-x 4} and @kbd{C-x
-r}, are themselves prefix keys that lead to three-character key
+r}, are themselves prefix keys that lead to three-event key
sequences. There's no limit to the length of a key sequence, but in
practice people rarely use sequences longer than four events.
By contrast, you can't add more events onto a complete key. For
-example, the two-character sequence @kbd{C-f C-k} is not a key, because
+example, the two-event sequence @kbd{C-f C-k} is not a key, because
the @kbd{C-f} is a complete key in itself. It's impossible to give
@kbd{C-f C-k} an independent meaning as a command. @kbd{C-f C-k} is two
key sequences, not one.@refill
All told, the prefix keys in Emacs are @kbd{C-c}, @kbd{C-h},
@kbd{C-x}, @kbd{C-x @key{RET}}, @kbd{C-x @@}, @kbd{C-x a}, @kbd{C-x n}, @w{@kbd{C-x
-r}}, @kbd{C-x v}, @kbd{C-x 4}, @kbd{C-x 5}, @kbd{C-x 6}, @key{ESC},
-@kbd{M-g} and @kbd{M-j}. But this list is not cast in concrete; it is
+r}}, @kbd{C-x v}, @kbd{C-x 4}, @kbd{C-x 5}, @kbd{C-x 6}, @key{ESC}, and
+@kbd{M-g}. But this list is not cast in concrete; it is
just a matter of Emacs's standard key bindings. If you customize Emacs,
you can make new prefix keys, or eliminate these. @xref{Key Bindings}.
If you do make or eliminate prefix keys, that changes the set of
possible key sequences. For example, if you redefine @kbd{C-f} as a
prefix, @kbd{C-f C-k} automatically becomes a key (complete, unless you
-define it too as a prefix). Conversely, if you remove the prefix
+define that too as a prefix). Conversely, if you remove the prefix
definition of @kbd{C-x 4}, then @kbd{C-x 4 f} (or @kbd{C-x 4
@var{anything}}) is no longer a key.
Typing the help character (@kbd{C-h} or @key{F1}) after a prefix
-character displays a list of the commands starting with that prefix.
-There are a few prefix characters for which @kbd{C-h} does not
+key displays a list of the commands starting with that prefix.
+There are a few prefix keys for which @kbd{C-h} does not
work---for historical reasons, they have other meanings for @kbd{C-h}
which are not easy to change. But @key{F1} should work for all prefix
-characters.
-
+keys.
+
@node Commands, Text Characters, Keys, Top
@section Keys and Commands
after mentioning the key that runs it. For example, we will say that
``The command @kbd{C-n} (@code{next-line}) moves point vertically
down,'' meaning that @code{next-line} is a command that moves vertically
-down and @kbd{C-n} is a key that is standardly bound to it.
+down, and @kbd{C-n} is a key that is normally bound to it.
While we are on the subject of information for customization only,
it's a good time to tell you about @dfn{variables}. Often the
@cindex characters (in text)
Text in Emacs buffers is a sequence of 8-bit bytes. Each byte can
-hold a single ASCII character. Both ASCII control characters (octal
-codes 000 through 037, and 0177) and ASCII printing characters (codes
-040 through 0176) are allowed; however, non-ASCII control characters
+hold a single @acronym{ASCII} character. Both @acronym{ASCII} control characters (octal
+codes 000 through 037, and 0177) and @acronym{ASCII} printing characters (codes
+040 through 0176) are allowed; however, non-@acronym{ASCII} control characters
cannot appear in a buffer. The other modifier flags used in keyboard
input, such as Meta, are not allowed in buffers either.
- Some ASCII control characters serve special purposes in text, and have
+ Some @acronym{ASCII} control characters serve special purposes in text, and have
special names. For example, the newline character (octal code 012) is
used in the buffer to end a line, and the tab character (octal code 011)
is used for indenting to the next tab stop column (normally every 8
columns). @xref{Text Display}.
- Non-ASCII printing characters can also appear in buffers. When
-multibyte characters are enabled, you can use any of the non-ASCII
+ Non-@acronym{ASCII} printing characters can also appear in buffers. When
+multibyte characters are enabled, you can use any of the non-@acronym{ASCII}
printing characters that Emacs supports. They have character codes
starting at 256, octal 0400, and each one is represented as a sequence
of two or more bytes. @xref{International}. Single-byte characters
with codes 128 through 255 can also appear in multibyte buffers.
If you disable multibyte characters, then you can use only one
-alphabet of non-ASCII characters, but they all fit in one byte. They
+alphabet of non-@acronym{ASCII} characters, but they all fit in one byte. They
use codes 0200 through 0377. @xref{Single-Byte Character Support}.
+
+@ifnottex
+@lowersections
+@end ifnottex
+
+@ignore
+ arch-tag: 9be43eef-d1f4-4d03-a916-c741ea713a45
+@end ignore