[Groff] Unix roff vs. groff: .in in ms?

[Jonathan Lennox]

I'm trying to use some roff code written for Unix (n)roff with groff, and
I'm running into a problem.

Unix roff's ms macro package seem to have no problem with allowing me to use
the .in directive, and the ms paragraph indentation directive are applied
relative to it.  Groff's ms, on the other hand, performs an absolute .in at
every .LP directive, and so my global intentation gets wiped out.

What I'd like is for paragraph bodies to be indented by 3 characters in
nroff output, but for section headers to still be left-justified.  (I'm
generating Internet-Drafts.)

This roff source is actually autogenerated, because nroff is the best tool
to usefully create sensibly formatted plain-text output of the kind needed
for Internet-Drafts.  I can change the autogenerator somewhat, but not
hugely.

What's the best way to do this in a way that's compatible both with the Unix
and the GNU ms macros?  Is there a macro I can define which I can globally
use to replace .in with the semantics I expect?

Thanks!

-- 
Jonathan Lennox
address@hidden