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elisp: Meta-Char Syntax

 
 2.3.3.4 Meta-Character Syntax
 .............................
 
 A “meta character” is a character typed with the <META> modifier key.
 The integer that represents such a character has the 2**27 bit set.  We
 use high bits for this and other modifiers to make possible a wide range
 of basic character codes.
 
    In a string, the 2**7 bit attached to an ASCII character indicates a
 meta character; thus, the meta characters that can fit in a string have
 codes in the range from 128 to 255, and are the meta versions of the
 ordinary ASCII characters.  Strings of Events, for details about
 <META>-handling in strings.
 
    The read syntax for meta characters uses ‘\M-’.  For example, ‘?\M-A’
 stands for ‘M-A’.  You can use ‘\M-’ together with octal character codes
 (see below), with ‘\C-’, or with any other syntax for a character.
 Thus, you can write ‘M-A’ as ‘?\M-A’, or as ‘?\M-\101’.  Likewise, you
 can write ‘C-M-b’ as ‘?\M-\C-b’, ‘?\C-\M-b’, or ‘?\M-\002’.
 

Info Catalog elisp: Ctl-Char Syntax elisp: Character Type elisp: Other Char Bits