New Features for Reading Input

• The function set-input-mode now takes four arguments. The last argument is optional. Their names are interrupt, flow, meta and quit. The argument interrupt says whether to use interrupt-driven input. Non-nil means yes, and nil means no (use CBREAK mode). The argument flow says whether to enable terminal flow control. Non-nil means yes. The argument meta controls support for input character codes above 127. If meta is t, Emacs converts characters with the 8th bit set into Meta characters. If meta is nil, Emacs disregards the 8th bit; this is necessary when the terminal uses it as a parity bit. If meta is neither t nor nil, Emacs uses all 8 bits of input unchanged. This is good for terminals using European 8-bit character sets. If quit non-nil, it is the character to use for quitting. (Normally this is C-g.)
• The variable meta-flag has been deleted; use set-input-mode to enable or disable support for a META key. This change was made because set-input-mode can send the terminal the appropriate commands to enable or disable operation of the META key.
• The new variable extra-keyboard-modifiers lets Lisp programs "press" the modifier keys on the keyboard. The value is a bit mask:

  1

  The SHIFT key.

  2

  The LOCK key.

  4

  The CTL key.

  8

  The META key.

  When you use X windows, the program can press any of the modifier keys in this way. Otherwise, only the CTL and META keys can be virtually pressed.
• You can use the new function keyboard-translate to set up keyboard-translate-table conveniently.
• Y-or-n questions using the y-or-n-p function now accept C-] (usually mapped to abort-recursive-edit) as well as C-g to quit.
• The variable num-input-keys is the total number of key sequences that the user has typed during this Emacs session.
• A new Lisp variable, function-key-map, holds a keymap which describes the character sequences sent by function keys on an ordinary character terminal. This uses the same keymap data structure that is used to hold bindings of key sequences, but it has a different meaning: it specifies translations to make while reading a key sequence. If function-key-map "binds" a key sequence k to a vector v, then when k appears as a subsequence anywhere in a key sequence, it is replaced with v. For example, VT100 terminals send ESC O P when the "keypad" PF1 key is pressed. Thus, on a VT100, function-key-map should "bind" that sequence to [pf1]. This specifies translation of ESC O P into PF1 anywhere in a key sequence. Thus, typing C-c PF1 sends the character sequence C-c ESC O P, but read-key-sequence translates this back into C-c PF1, which it returns as the vector [?\C-c PF1]. Entries in function-key-map are ignored if they conflict with bindings made in the minor mode, local, or global keymaps. The value of function-key-map is usually set up automatically according to the terminal's Terminfo or Termcap entry, and the terminal-specific Lisp files. Emacs comes with a number of terminal-specific files for many common terminals; their main purpose is to make entries in function-key-map beyond those that can be deduced from Termcap and Terminfo.
• The variable key-translation-map works like function-key-map except for two things:
  • key-translation-map goes to work after function-key-map is finished; it receives the results of translation by function-key-map.
  • key-translation-map overrides actual key bindings.
  The intent of key-translation-map is for users to map one character set to another, including ordinary characters normally bound to self-insert-command.