The event-reading functions invoke the current input method, if any (see Input Methods). If the value of
input-method-function is non-
nil, it should be a function; when
read-event reads a printing character (including
SPC) with no modifier bits, it calls that function, passing the character as an argument.
If this is non-
nil, its value specifies the current input method function.
Warning: don’t bind this variable with
let. It is often buffer-local, and if you bind it around reading input (which is exactly when you would bind it), switching buffers asynchronously while Emacs is waiting will cause the value to be restored in the wrong buffer.
The input method function should return a list of events which should be used as input. (If the list is
nil, that means there is no input, so
read-event waits for another event.) These events are processed before the events in
unread-command-events (see Event Input Misc). Events returned by the input method function are not passed to the input method function again, even if they are printing characters with no modifier bits.
If the input method function calls
read-key-sequence, it should bind
nil first, to prevent recursion.
The input method function is not called when reading the second and subsequent events of a key sequence. Thus, these characters are not subject to input method processing. The input method function should test the values of
overriding-terminal-local-map; if either of these variables is non-
nil, the input method should put its argument into a list and return that list with no further processing.