typemap variables docs

[Scott Lanning]

Is it documented somewhere which variables are
available to typemaps and what they are?
Like $arg, $var, $type, but I also see different
and mysterious ones. I tried looking around ExtUtils,
but ran in circles.
  I find myself copy/paste/editing typemaps a zillion times,
but I think I could surely doing it much more concisely
if I knew which variable to use.