[Groff] The \D request in nroff and troff modes

[Anton Shepelev]

Hello all,

I  have  found what may be a bug either in tbl or in
groff's \D request. Or I don't understand how either
works.  The  same piece of code typesets differently
in troff and nroff modes:

   .ll 36n
   .br
   The line below should be the current line-length:
   .br
   \D'l \n[.l]u 0'
   .br
   Note how the left margin of this text corresponds
   with the left end of the above line in troff mode
   and is one symbol shorter in nroff mode. The
   table below has exactly the same problem with its
   rulers:
   .TS
   expand tab(@);
   l l.
   _
   address@hidden
   _
   .TE

When typeset in nroff mode, the lenght  of  the  ta-
ble's  rulers, as well as of the line drawn with the
\D request, is one syblol more than the actual  line
length,  while  in nroff mode they are well aligned.
Below is the output of nroff:

   The line below should be the current
   line-length:
   -------------------------------------
   Note how the  left  margin  of  this
   text  corresponds  with the left end
   of the above line in troff mode  and
   is one symbol shorter in nroff mode.
   The table below has exactly the same
   problem with its rulers:
   -------------------------------------
   Left                           Right
   -------------------------------------

Is this the correct behaviour of  \D?  If  so,  then
this should be comensated for somehow in tbl, for it
uses the same request to tables' rulers.

Anton