elisp: Other Char Bits
2.3.3.5 Other Character Modifier Bits
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The case of a graphic character is indicated by its character code; for
example, ASCII distinguishes between the characters ‘a’ and ‘A’. But
ASCII has no way to represent whether a control character is upper case
or lower case. Emacs uses the 2**25 bit to indicate that the shift key
was used in typing a control character. This distinction is possible
only when you use X terminals or other special terminals; ordinary text
terminals do not report the distinction. The Lisp syntax for the shift
bit is ‘\S-’; thus, ‘?\C-\S-o’ or ‘?\C-\S-O’ represents the
shifted-control-o character.
The X Window System defines three other modifier bits that can be set
in a character: “hyper”, “super” and “alt”. The syntaxes for these bits
are ‘\H-’, ‘\s-’ and ‘\A-’. (Case is significant in these prefixes.)
Thus, ‘?\H-\M-\A-x’ represents ‘Alt-Hyper-Meta-x’. (Note that ‘\s’ with
no following ‘-’ represents the space character.) Numerically, the bit
values are 2**22 for alt, 2**23 for super and 2**24 for hyper.
Info Catalog
elisp: Meta-Char Syntax
elisp: Character Type