Re: Need background on design of groff character classes

On Mon, Nov 17, 2025 at 4:34 PM G. Branden Robinson
<[email protected]> wrote:
> I won't attempt to completely characterize Dave's position, but it
> differs.  I think it's fair to say that he envisions classes as having
> additional properties compared to my view.

I don't really envision anything.  I note that the behavior I've
observed since first using classes in 2011 differs from the model
you've presented, and in a way that makes the language more useful
than how you seem to want it to work.

I'd use a simpler example than the one you presented to make my point.

Suppose you want the em dash to have the end-of-sentence property (in
character flags parlance, having flag 1 set).  You might be tempted to
say:

.cflags 1 \[em]

And this would work to set its end-of-sentence property--but it would
have the side effect of overwriting the flag (4) that \[em] already
had set.

So instead you might do this:

.class [EOS] \[em]
.cflags 1 \C'[EOS]'

This has, since the first groff release where .class was introduced,
had the observable effect of making the em dash recognized as ending a
sentence (flag 1) while retaining its breaking behavior (as encoded in
flag 4).

Why is this significant?  Because if you want to add a flag to a
character's existing flags, there is no other way to do it.  The
.cflags request only overwrites all existing flags; it does not have a
syntax to preserve flags while adding a new one.  And the language has
no mechanism for returning a character's current flags.  (Recent,
post-1.23 groff builds include a request that lets you dump the flags,
along with much other info about a character, to stderr, but groff is
still unable to access that value from within a document.)  So you
can't compute the flag you want to add ANDed with any existing flags.

So the current .class behavior provides useful functionality.  Thus I
presumed the behavior was intended; but even if not, I see no benefit
to altering it to fit a different model that makes impossible an
operation that is currently possible.