[csswg-drafts] [css-fonts-5] Computed value of `font-size-adjust: from-font` (#9050)

jfkthame has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-fonts-5] Computed value of `font-size-adjust: from-font` ==
[The current spec](https://drafts.csswg.org/css-fonts-5/#font-size-adjust-prop) says that the computed value of `font-size-adjust` is

> the keyword [none](https://drafts.csswg.org/css-fonts-5/#valdef-font-size-adjust-none), or a pair of a metric keyword and a [`<number>`](https://drafts.csswg.org/css-values-4/#number-value)

and for [the `from-font` keyword](https://drafts.csswg.org/css-fonts-5/#valdef-font-size-adjust-from-font) it confirms that this

> Computes to the [`<number>`](https://drafts.csswg.org/css-values-4/#number-value) corresponding to the specified metric of the [first available font](https://drafts.csswg.org/css-fonts-4/#first-available-font).

As I'm looking at [implementing this in Gecko](https://bugzilla.mozilla.org/show_bug.cgi?id=1708240), the [question arose](https://phabricator.services.mozilla.com/D182449#6035547) as to whether the behavior in the spec is really what is desired here.

Note that the behavior currently implemented in WebKit (and expected by a WPT testcase) is different. Using current Safari Technology Preview:
```
> document.body.style.fontSizeAdjust = "from-font"
< "from-font"
> window.getComputedStyle(document.body).fontSizeAdjust
< "from-font"
```
we see that the computed value is the `from-font` keyword; it is *not* resolved to a `<number>` at computed-value time.

@litherum @svgeesus Should the spec be changed to reflect this, or should we file a bug against WebKit and proceed with implementing what the spec says?

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/9050 using your GitHub account


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Received on Monday, 10 July 2023 13:05:07 UTC