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(elisp)Invoking the Input Method

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Invoking the Input Method
-------------------------

   The event-reading functions invoke the current input method, if any
(Note: 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.

 - Variable: input-method-function
     If this is non-`nil', its value specifies the current input method
     function.

     *Note:* 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' (Note: 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-event' or
`read-key-sequence', it should bind `input-method-function' to `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-local-map' and
`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.