Describing Characters - GNU Emacs Lisp Reference Manual

These functions convert events, key sequences, or characters to textual descriptions. These descriptions are useful for including arbitrary text characters or key sequences in messages, because they convert non-printing and whitespace characters to sequences of printing characters. The description of a non-whitespace printing character is the character itself.

— Function: key-description sequence

This function returns a string containing the Emacs standard notation for the input events in sequence. The argument sequence may be a string, vector or list. See Input Events, for more information about valid events. See also the examples for single-key-description, below.

— Function: single-key-description event &optional no-angles

This function returns a string describing event in the standard Emacs notation for keyboard input. A normal printing character appears as itself, but a control character turns into a string starting with ‘C-’, a meta character turns into a string starting with ‘M-’, and space, tab, etc. appear as ‘SPC’, ‘TAB’, etc. A function key symbol appears inside angle brackets ‘<...>’. An event that is a list appears as the name of the symbol in the car of the list, inside angle brackets.
If the optional argument no-angles is non-nil, the angle brackets around function keys and event symbols are omitted; this is for compatibility with old versions of Emacs which didn't use the brackets.
          (single-key-description ?\C-x)
               => "C-x"
          (key-description "\C-x \M-y \n \t \r \f123")
               => "C-x SPC M-y SPC C-j SPC TAB SPC RET SPC C-l 1 2 3"
          (single-key-description 'delete)
               => "<delete>"
          (single-key-description 'C-mouse-1)
               => "<C-mouse-1>"
          (single-key-description 'C-mouse-1 t)
               => "C-mouse-1"
     

— Function: text-char-description character

This function returns a string describing character in the standard Emacs notation for characters that appear in text—like single-key-description, except that control characters are represented with a leading caret (which is how control characters in Emacs buffers are usually displayed).
          (text-char-description ?\C-c)
               => "^C"
          (text-char-description ?\M-m)
               => "M-m"
          (text-char-description ?\C-\M-m)
               => "M-^M"
     

— Function: read-kbd-macro string

This function is used mainly for operating on keyboard macros, but it can also be used as a rough inverse for key-description. You call it with a string containing key descriptions, separated by spaces; it returns a string or vector containing the corresponding events. (This may or may not be a single valid key sequence, depending on what events you use; see Keymap Terminology.)

24.4 Describing Characters for Help Messages