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
it.
If there is no @key{META} key, you can still type Meta characters
-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}. @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
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
keys.
-
+
@node Commands, Text Characters, Keys, Top
@section Keys and Commands
@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