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
