mdn
css.properties.font-variant-position - Safari doesn't support synthesizing
What type of issue is this?
Browser bug (a bug with a feature that may impact site compatibility)
What information was incorrect, unhelpful, or incomplete?
Safari does support font-variant-position, but doesn't do synthesizing[^1] as described in the entry for the CSS feature.
[^1]: From the MDN entry: "[...] if one character in the run doesn't have such a typographically-enhanced glyph, the whole set of characters of the run is rendered using a fallback method, synthesizing these glyphs."
What browsers does this problem apply to, if applicable?
Safari
What did you expect to see?
Safari browsers should have a note saying something like "Fallback synthesizing not supporting".
Did you test this? If so, how?
Yes:
In Safari, go to https://developer.mozilla.org/en-US/docs/Web/CSS/font-variant-position. Here, the playground will use a default system font (not a webfont) which most likely cannot support superscript or subscript glyphs.
In addition, http://wpt.live/css/css-fonts/font-variant-position-05.html also shows the behaviour: Here the "." glyph is not contained as a superscript in the font, and thus the whole line should be rendered using synthesized superscript.
Tested in Safari 16.6 for macOS.
Can you link to any release notes, bugs, pull requests, or MDN pages related to this?
The Chrome "Intent to Ship" issue mentions this behavior in Safari: https://groups.google.com/a/chromium.org/g/blink-dev/c/wQ_8T-AXLFA/m/IbL4wlAMBAAJ
The behaviour can also be seen in Web Platform Tests: https://wpt.fyi/results/css/css-fonts?label=master&label=experimental&aligned&q=font-variant-position
Do you have anything more you want to share?
In addition, Chrome 117+ now also supports font-variant-position, but also without support for synthesizing 😢 See https://wpt.fyi/results/css/css-fonts?q=font-variant-position&run_id=5157154199175168&run_id=5123568829988864&run_id=5154818978480128&run_id=5143779570352128&run_id=5079513135841280&run_id=5162670212251648
MDN URL
https://developer.mozilla.org/en-US/docs/Web/CSS/font-variant-position
MDN metadata
MDN page report details
- Query:
css.properties.font-variant-position - Report started: 2023-08-31T07:00:28.139Z
What is the process for removing this entirely from Baseline until full support is released? Full support for the property is very evidently incomplete in WebKit and Chromium, but more to the point lack of support for the synthesis requirement is potentially harmful to the visual semantics, and therefore cannot be considered safe to use at this point in time.
I can reproduce that https://wpt.live/css/css-fonts/font-variant-position-05.html does not render correctly in Chrome 135 and Safari 18.4, while it does in Firefox 137.
We should add a behavioral subfeature for this, which refers to this aspect of the CSS Fonts spec (ref):
if a variant glyph is not available for all the characters in the run, simulated glyphs should be synthesized for all characters using reduced forms of the glyphs that would be used without this feature applied