One of the main ways to extend exmh is to write your own code and call it from exmh.
Such code is stored in a personal directory that can be in one of two places. Exmh will search in order for these directories
The first of these directories that exists will be used.
Regenerating tclIndex
Whenever you do anything that adds or deletes a Tcl proc to any file in your library directory you must regenerate the tclIndex file. That can be done as follows: