*command
**
format  : preproc "from/a,to/a,header/k,ver/s,with/k"
author  : MFR
purpose : conditional compilation tag stripping

          The preproc command processes conditional compilation tags of the
form $<tag $>tag, etc.

          from   : input file
          to     : destination file
          header : optional header file   (concatentated to front of input)
          with   : optional header string (concatentated to front of input)
                   (ie., input is <with>+<header>+<from>)
          ver    : will give list of tags and settings at end

          Tags should be of the form $<tag $>tag and $<tag' $>tag'. They may
be set by $$tag:=true, $$tag:=false, $$tag:=$$tag2, or $$tag:=$$tag2'. Other
expressions are not allowed.  There is almost no error checking. Tags may be
nested.


