[bug #64728] diversion widths reported when using eqn mark/lineup feature inconsistent with Heirloom

[G. Branden Robinson]

Update of bug#64728 (group groff):

             Assigned to:                gbranden => None                   

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Follow-up Comment #6:

The information needed here is a gathering of information about various *roff
implementations.

This stuff looks like it's so ill-defined that I think we want to check out
Seventh Edition Unix troff as well (which we can do with `tm` requests even if
the _program_ output is incomprehensible).

We should consider V7 troff, DWB 3.3, Heirloom Doctools, and possibly
plan9port and neatroff.

Do the diversion measurement registers `dn` and `dl` measure:

* net motion of the drawing position,
* maximal motion of the drawing position relative to that where the diversion
started,
or
* maximal bounds of spilled ink relative to the drawing position where the
diversion started?

Negative motions seem ill-defined with only two registers.  Presumably this is
why all `sp` requests mean `sp 1` inside diversions, but possibly this insight
was insufficiently generalized back in the day.

Unassigning from self because I'm not the only person who can gather such
information.


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