Re: [csswg-drafts] [css-fonts-5] font-size-adjust with missing metrics (#6384)

> If that's good enough for the cap unit, I'd say it's good enough for font-size-adjust as well. And if not, we should fix it globally, not introduce divergence between the unit and the size-adjust factor.

I can see the point about keeping consistency in mapping back to the metrics values and not branching in this spec based on a specific metric's existence or not. On the other hand, we have an opportunity here to not build on shaky foundations. A good design and spec tightens the behavior for the realistic scenario in which a specific metric is not available, that's possible because some metrics are optional in OpenType/OFF. We can make the start here and define no-adjustment as the behavior for unavailable metric.

As a consequence, as this topic is relevant for interop 2024, this means, we can't test fallback behavior in any WPT test as every UA will have divergent fallback behavior. Positively phrased: WPT tests for font-size-adjust can only be testing with fonts for which the respective tested metric exists.

In particular, as there is no fallback definition for `ic-height`, we can't test fallback behavior for that either in an interoperable way.


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Received on Wednesday, 8 May 2024 08:21:31 UTC