Re: [Groff] Question about .trunc

[Peter Schaffter]

On Thu, Nov 03, 2016, Tadziu Hoffmann wrote:
> 
> If you request a certain amount of vertical space,
> 
>   .sp <wantedspace>
> 
> and the distance to the next trap (available in register .t)
> is smaller than this, the trap is sprung and .trunc is set to
> 
>   <wantedspace> - <distance-to-trap>
> 
> i.e., the amount truncated (not output) from <wantedspace>.
> (See attached example; use -Tps and paper size a4.)
 
When I remove the .sp 10v from the file, i.e. allow text to flow
uninterrupted, .trunc reports '0', the behaviour I asked about.  Is
this a buglet in the documentation, then?  It says:

  "A read-only register containing the amount of vertical space
  truncated by the most recently sprung vertical position trap..."

Should it say, instead:

"...the amount of vertical space truncated from a .sp request
                                           ^^^^^^^^^^^^^^^^^^
by the most recently sprung vertical position trap..."

That would seem to be the case.  Doesn't help with the fact that
something like .trunc for any and all truncated vertical space,
including trucated \n[.v], would be useful for the purpose of
calculating vertical flex-space in a two-pass scenario.

-- 
Peter Schaffter
http://www.schaffter.ca