[groff] soelim: Ignoring Some ’so’ Requests

[Jeff Conrad]

If a file isn’t needed by a troff preprocessor, it is sometimes
desirable to have an ‘so’ request ignored by soelim(1).  A traditional
idiom for doing this was calling ‘so’ with the no-break control
character, e.g.,

'so /usr/lib/tmac/tmac.m

This probably wouldn’t be the preferred way of doing things anymore, but
a person might still encounter some old troff source and wonder “What’s
going on here?”

I can’t find any mention of this in the groff documentation.  In a quick
Google search, only the IBM man page seems to mention it.

The careful reader of the groff soelim man page will see that the same
thing can be accomplished by putting whitespace between the standard
control character and the request (e.g., “. so”), and examining the
soelim source makes clear that only “.so” will cause a file to be
included.

I managed to see this, but I was looking for it.  Would it be as easy
for someone who didn’t already know the answer?  Perhaps a brief
description of how this works—preferably not just in the soelim man
page—would be helpful.

Jeff Conrad