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revision 1.13 by miles, Mon Sep 1 15:45:45 2003 UTC revision 1.14 by eliz, Sun Nov 2 07:01:01 2003 UTC
# Line 15  how Emacs interprets your keyboard and m Line 15  how Emacs interprets your keyboard and m
15  @cindex input with the keyboard  @cindex input with the keyboard
16  @cindex keyboard input  @cindex keyboard input
17  @cindex character set (keyboard)  @cindex character set (keyboard)
18  @cindex ASCII  @cindex @acronym{ASCII}
19  @cindex C-  @cindex C-
20  @cindex Control  @cindex Control
21  @cindex control characters  @cindex control characters
22    
23    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
24  input; it also accepts non-character input events including function  input; it also accepts non-character input events including function
25  keys and mouse button actions.  keys and mouse button actions.
26    
27    ASCII consists of 128 character codes.  Some of these codes are    @acronym{ASCII} consists of 128 character codes.  Some of these codes are
28  assigned graphic symbols such as @samp{a} and @samp{=}; the rest are  assigned graphic symbols such as @samp{a} and @samp{=}; the rest are
29  control characters, such as @kbd{Control-a} (usually written @kbd{C-a}  control characters, such as @kbd{Control-a} (usually written @kbd{C-a}
30  for short).  @kbd{C-a} gets its name from the fact that you type it by  for short).  @kbd{C-a} gets its name from the fact that you type it by
31  holding down the @key{CTRL} key while pressing @kbd{a}.  holding down the @key{CTRL} key while pressing @kbd{a}.
32    
33    Some ASCII control characters have special names, and most terminals    Some @acronym{ASCII} control characters have special names, and most terminals
34  have special keys you can type them with: for example, @key{RET},  have special keys you can type them with: for example, @key{RET},
35  @key{TAB}, @key{DEL} and @key{ESC}.  The space character is usually  @key{TAB}, @key{DEL} and @key{ESC}.  The space character is usually
36  referred to below as @key{SPC}, even though strictly speaking it is a  referred to below as @key{SPC}, even though strictly speaking it is a
37  graphic character whose graphic happens to be blank.  Some keyboards  graphic character whose graphic happens to be blank.  Some keyboards
38  have a key labeled ``linefeed'' which is an alias for @kbd{C-j}.  have a key labeled ``linefeed'' which is an alias for @kbd{C-j}.
39    
40    Emacs extends the ASCII character set with thousands more printing    Emacs extends the @acronym{ASCII} character set with thousands more printing
41  characters (@pxref{International}), additional control characters, and a  characters (@pxref{International}), additional control characters, and a
42  few more modifiers that can be combined with any character.  few more modifiers that can be combined with any character.
43    
44    On ASCII terminals, there are only 32 possible control characters.    On @acronym{ASCII} terminals, there are only 32 possible control characters.
45  These are the control variants of letters and @samp{@@[]\^_}.  In  These are the control variants of letters and @samp{@@[]\^_}.  In
46  addition, the shift key is meaningless with control characters:  addition, the shift key is meaningless with control characters:
47  @kbd{C-a} and @kbd{C-A} are the same character, and Emacs cannot  @kbd{C-a} and @kbd{C-A} are the same character, and Emacs cannot
# Line 117  Reference Manual}, for more information. Line 117  Reference Manual}, for more information.
117  programming, but simply want to redefine the meaning of some characters  programming, but simply want to redefine the meaning of some characters
118  or non-character events, see @ref{Customization}.  or non-character events, see @ref{Customization}.
119    
120    ASCII terminals cannot really send anything to the computer except    @acronym{ASCII} terminals cannot really send anything to the computer except
121  ASCII characters.  These terminals use a sequence of characters to  @acronym{ASCII} characters.  These terminals use a sequence of characters to
122  represent each function key.  But that is invisible to the Emacs user,  represent each function key.  But that is invisible to the Emacs user,
123  because the keyboard input routines recognize these special sequences  because the keyboard input routines recognize these special sequences
124  and convert them to function key events before any other part of Emacs  and convert them to function key events before any other part of Emacs
# Line 243  variables will make sense.  @xref{Variab Line 243  variables will make sense.  @xref{Variab
243  @cindex characters (in text)  @cindex characters (in text)
244    
245    Text in Emacs buffers is a sequence of 8-bit bytes.  Each byte can    Text in Emacs buffers is a sequence of 8-bit bytes.  Each byte can
246  hold a single ASCII character.  Both ASCII control characters (octal  hold a single @acronym{ASCII} character.  Both @acronym{ASCII} control characters (octal
247  codes 000 through 037, and 0177) and ASCII printing characters (codes  codes 000 through 037, and 0177) and @acronym{ASCII} printing characters (codes
248  040 through 0176) are allowed; however, non-ASCII control characters  040 through 0176) are allowed; however, non-@acronym{ASCII} control characters
249  cannot appear in a buffer.  The other modifier flags used in keyboard  cannot appear in a buffer.  The other modifier flags used in keyboard
250  input, such as Meta, are not allowed in buffers either.  input, such as Meta, are not allowed in buffers either.
251    
252    Some ASCII control characters serve special purposes in text, and have    Some @acronym{ASCII} control characters serve special purposes in text, and have
253  special names.  For example, the newline character (octal code 012) is  special names.  For example, the newline character (octal code 012) is
254  used in the buffer to end a line, and the tab character (octal code 011)  used in the buffer to end a line, and the tab character (octal code 011)
255  is used for indenting to the next tab stop column (normally every 8  is used for indenting to the next tab stop column (normally every 8
256  columns).  @xref{Text Display}.  columns).  @xref{Text Display}.
257    
258    Non-ASCII printing characters can also appear in buffers.  When    Non-@acronym{ASCII} printing characters can also appear in buffers.  When
259  multibyte characters are enabled, you can use any of the non-ASCII  multibyte characters are enabled, you can use any of the non-@acronym{ASCII}
260  printing characters that Emacs supports.  They have character codes  printing characters that Emacs supports.  They have character codes
261  starting at 256, octal 0400, and each one is represented as a sequence  starting at 256, octal 0400, and each one is represented as a sequence
262  of two or more bytes.  @xref{International}.  Single-byte characters  of two or more bytes.  @xref{International}.  Single-byte characters
263  with codes 128 through 255 can also appear in multibyte buffers.  with codes 128 through 255 can also appear in multibyte buffers.
264    
265    If you disable multibyte characters, then you can use only one    If you disable multibyte characters, then you can use only one
266  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
267  use codes 0200 through 0377.  @xref{Single-Byte Character Support}.  use codes 0200 through 0377.  @xref{Single-Byte Character Support}.
268    
269  @ignore  @ignore

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