Re: GNU eqn clarifications and reforms

[Douglas McIlroy]

>  I think moving to
>          .EQ
>          delim ##
>          .EN
>  is an alternative which is easier to justify (and explain).

$$ is etched into my fingertips; @@ is the fallback when
I need to protect $1 and the like, typically for pic code
that contains its own macros together with eqn constructs.

## has the virtue of not colliding with other eqn constructs
or with groff macro definitions. It does collide with groff
color specs and \# comments and with pic comments, so
it's not a panacea, but seems better than $$.

@@ may deserve consideration. The only collisions that
come to mind are with the esoteric groff escape \$@.and
with mentions of email addresses or shell scripts.
Unfortunately, it is visually intrusive.

You may also want to make a recommendation for
delimiting bodies of eqn macros. I use %%--not
perfect, but any conflicting groff constructs will be right
there in full view.

Doug