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Re: Should vertical motions be in vees or ems? Where does the baseline g

From: Ralph Corderoy
Subject: Re: Should vertical motions be in vees or ems? Where does the baseline go?
Date: Tue, 16 Nov 2021 17:48:02 +0000

Hi Dave,

> > > What would an ideal model of output from the above input look like?
> >
> > What's the argument against CSTR 54's section 11.1 definitions being
> > the ideal?
> Two are:
> - General typographic convention is to measure vertical motions in
> v's, not m's.  CSTR #54's definitions of \u, \d, and \r do not align
> with this common expectation.

That shipped sailed in the Seventies.  :-)

> - CSTR #54 is not even internally consistent in this regard: most
> vertical motions are specified in v's.  \u, \d, and \r are outliers
> even in troff-land.


> Determining what historical troff did is tougher unless you have a
> Graphic Systems C/A/T lying around: a code analysis in
> concluded CSTR #54 was
> incorrect about troff's behavior on this point.  But Heirloom troff's
> behavior, if a legitimate proxy for AT&T troff, calls that conclusion
> into question.

The analysis stops with a guess which is wrong.  I've added a comment to
the issue:

    CSTR 54 is correct.  Branden's 'guess' is wrong and no change from
    Bell Labs troff's normal and documented behaviour should be made
    based on it.  vflag is used to indicate the motion is vertical.
    It is nothing to do with forcing a unit calculation to be vees.
    The code of makem(), quoted but not analysed above, makes this

    groff's behaviour and documentation should copy both CSTR 54 and the
    historic behaviour which as [they] are in agreement are therefore

\u, \d, and \r are ems.  If that's not what's wanted then something else
should be used; they should not be changed.

Cheers, Ralph.

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