[HTML-CSS][FF][MacOS] supscripts can be too close to base

[pkra]

Reported at https://stackoverflow.com/questions/47344711/mathjax-exponent-too-close-from-term.

I could reproduce this on MacOS 10.12, FF 57.

It might be specific to STIX fonts (CommonHTML and SVG are fine).

[dpvc]

As you suspected, this is due to the font metrics of the STIX fonts. The italic "j" extends to the left of its bounding box by .124em (which amounts to a pixel or two at usual sizes), while the TeX font's italic "j" only extends to the left by .012em (1/10 as much). So when the superscript "j" is placed net to the "v" in the STIX fonts, the bottom of the "j" extends to the left of its bounding box by a few pixels, and bumps the base "v". This is inherent in the metrics of the STIX fonts. I would be hesitant to change the metrics for fear for making other situations worse.

[dpvc]

I've marked it "accepted" but I'm not sure what else to mark it as, since there doesn't seem to be another applicable label. Should we have a "font bug" label?

[pkra]

Should we have a "font bug" label?

Sounds good to me but upstream is perhaps enough?

I've added this issue to the "a future font release" milestone because when we switch to STIX2 (which is really a new font) we can check if this kind of problem is resolved.

[dpvc]

"Upstream" is good, thanks.

Yes, checking the situation with STIX2 is a good idea.

[dpvc]

It turns out that this is probably actually due to the same issue as #1923. So I'm remarking this as a duplicate of that.

[dpvc]

Fixed by #1923.