If the macro returns a string or integer, this value
will be used in place of the original character typed,
and inserted at the cursor's position after the macro's
In particular, this allows for a return value of ""
(the empty string), in which case no insert occurs
after the macro.
This allows you to program (for example) word
completion as part of the type-in macro process,
without having to worry about dealing with left-over
If no value is returned, the behaviour is as before.