is used by many scripts. is used by some scripts, mostly within mtx_context which is part of conTeXt, but also for one or two others, such as match_parens, which are generally useful. The perl module Tk, which requires , is used by one of the scripts for ptex (Japanese vertical writing), can be used by a conTeXt texfind script, and is needed for texdoctk (a GUI interface for finding documentation files and opening them with the appropriate viewer).