Hi Mike,
> Groff starts off in no-space mode until either the .rs command or
> some text is output. no-space mode means any request for vertical
> spacing is ignored.
>
> I cannot find where this is explained in the documentation.
> Computing Science Technical Report No. 54
> Troff User's Manual
> hints at it, but ...
The table split across its pages 14/15 describing .ns and .rs both have
`space' as the second field, Initial value, stating space mode is the
default. Empirically, it seems correct.
$ nroff <<<foo | uniq -c
1 foo
65
$ printf '.sp 3.14i\nfoo\n' | nroff | uniq -c
19
1 foo
46
$
Cheers, Ralph.
