Re: [groff] 02/11: [docs]: Update discussion of `ss` request.

[G. Branden Robinson]

At 2023-05-19T21:30:31-0500, Dave Kemper wrote:
> Regarding the conventional space width, this patch added this
> parenthetical:
> 
> > current font's space width (usually one-third em for Western scripts)
> 
> But this claim is not reflected in the data for the fonts shipped with
> groff for the two most common typesetting devices, ps and pdf.
> 
> $ fgrep unitwidth font/devp*/DESC.in
> font/devpdf/DESC.in:unitwidth 1000
> font/devps/DESC.in:unitwidth 1000
> 
> So for these devices, 1/4 em would be 250 units, and 1/3 would be 333.
> The actual space widths for the fonts (pdf inherits the metrics from
> ps, I believe) are:

Yes, because the base fonts for PS and PDF are supposed to be metrically
compatible.  And in the early days, the font files themselves were often
identical, as I understand it.

> Disregarding the four monospace fonts, which require their own spacing
> rules, 29 of those fonts are closer to 1/4 em, and 5 of them to 1/3 em
> (though few are exactly either 1/4 or 1/3).
> 
> This aligns with what our friend Heraclitean River
> (http://web.archive.org/web/20171217060354/http://www.heracliteanriver.com/?p=324)
> observed in his research: "Margins became smaller [in the first half
> of the 20th century], and standard interword spaces often went from
> about 1/3 em to 1/4 em."

That's a resource that just keeps paying dividends.

> Incidentally, where the same parenthetical phrase is inserted into
> groff_diff(7), it introduces mismatched parentheses (not obvious as
> they go three levels deep).

Thanks, Dave.  I've fixed these problems in my working copy and they'll
be in my next push to master--a matter of hours, perhaps.

Regards,
Branden

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