elisp: Ctl-Char Syntax
2.3.3.3 Control-Character Syntax
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Control characters can be represented using yet another read syntax.
This consists of a question mark followed by a backslash, caret, and the
corresponding non-control character, in either upper or lower case. For
example, both ‘?\^I’ and ‘?\^i’ are valid read syntax for the character
‘C-i’, the character whose value is 9.
Instead of the ‘^’, you can use ‘C-’; thus, ‘?\C-i’ is equivalent to
‘?\^I’ and to ‘?\^i’:
?\^I ⇒ 9 ?\C-I ⇒ 9
In strings and buffers, the only control characters allowed are those
that exist in ASCII; but for keyboard input purposes, you can turn any
character into a control character with ‘C-’. The character codes for
these non-ASCII control characters include the 2**26 bit as well as the
code for the corresponding non-control character. Ordinary text
terminals have no way of generating non-ASCII control characters, but
you can generate them straightforwardly using X and other window
systems.
For historical reasons, Emacs treats the <DEL> character as the
control equivalent of ‘?’:
?\^? ⇒ 127 ?\C-? ⇒ 127
As a result, it is currently not possible to represent the character
‘Control-?’, which is a meaningful input character under X, using ‘\C-’.
It is not easy to change this, as various Lisp files refer to <DEL> in
this way.
For representing control characters to be found in files or strings,
we recommend the ‘^’ syntax; for control characters in keyboard input,
we prefer the ‘C-’ syntax. Which one you use does not affect the
meaning of the program, but may guide the understanding of people who
read it.
Info Catalog
elisp: General Escape Syntax
elisp: Character Type
elisp: Meta-Char Syntax