The spec reads:

"A component that supports on-the-spot text input needs to
    override this method to return an InputMethodRequests instance.
  At the same time, it has to add an input method listener."

suggest change to:
"A component that supports on-the-spot text input MAY
   override this method to return an InputMethodRequests instance
   WHILE ALSO adding an input method EVENT listener TO PROCESS EVENTS
   RECEIVED FROM INPUT METHODS."

Note that adding an input method event listener is, of course, not
required since events can also be processed by subclassing processInputMethodEvent, etc. Also, a developer in an extreme case
could implement there own on-the-spot text processing and input method
framework without subclassing this method.

note: with this clarification, the cross reference concern expressed in
bug 4115939 may be lessened.