nroff terminal file format wanted

[Robert Perlberg]

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Can anybody tell me what the format of the terminal description
files (tab files) in /usr/lib/term is?  It's nice that they built
that kind of configurability into nroff, but they didn't provide
any documentation (at least, I don't have any) on how to define
your own.  It would be nice if nroff used termcap (light bulb,
anyone?), but I realize that nroff predates termcap by a good
long stretch.

Thanks in advance

Robert Perlberg
Resource Dynamics Inc.
New York
philabs!rdin!rdin2!perl