2.3.3.5 Other Character Modifier Bits

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 terminals do not report the distinction to the computer in any way. 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.