Re: [groff] mark/lineup in eqn

[Doug McIlroy]

Sorry that my previous post was truncated. Here's what
I meant to say:

Fellow groffers, what do you think of generalizing the application
of "mark" and "lineup" in eqn to work in columns and piles as
well as in separately displayed equations.

A typical use of mark and lineup is to align = signs in
a sequence of equations. If the = signs signify steps of a
derivation, the equations should obviously be connected,
as in a pile. Displaying them separately, each with its
own EQ-EN, spreads them out vertically. One can play
with number registers (e.g. PD and DD in -ms) to try
to get the pile-like resultts, but it would much cleaner
if that could happen for free.

There is even a situation that EQ-EN can't handle, but
piles could:
.EQ L
xhortid mark = expression1
.EN
.EQ
longidentifier lineup = expression2
.EN
The marked place doesn't leave room for the subsequent
lineup. Piles, being typeset as a whole, would be
immune to this trouble.

Doug