[Groff] underlining in nroff

[Werner LEMBERG]

Dear friends,


currently, the underlining commands .ul and .cu does exactly the same
in nroff mode of gtroff.  This is incorrect, of course.  Nevertheless,
I have some questions how underlining works in Unix nroff and I ask
for help in answering this.

. What is the default underlining mode if I select an `italic' font
  (\fI) in nroff?  .ul or .cu?

. It seems to me that with the current ditroff output language, the
  difference between .ul and .cu can't be implemented in a
  straightforward manner.  The only solution with the current protocol
  is, for .ul, to switch back the font to \fR for all spaces so that
  space characters aren't underlined.  Or is there another solution?
  Can someone please check the ditroff output how the difference is
  implemented?


    Werner