[css-fonts] Clarify initial value of 'font-family'

[zcorpan]

https://drafts.csswg.org/css-fonts-4/#font-family-prop

Initial: depends on user agent

Is the keyword inherit a conforming initial value?

It seems like in WebKit, if you specify font-family: initial on an element, it will inherit the font-family from the parent, instead of getting whatever the root element would have if it had no author CSS specified.

http://software.hixie.ch/utilities/js/live-dom-viewer/saved/7116

The text "test" is in the fantasy font-family in WebKit, but in serif in Blink and Gecko.

In CSS2, there was no initial keyword, so this was not observable. But now it is, and it is not interoperable between browser engines.

Which behavior is intended? Like WebKit, or like Gecko/Blink? I assumed it would work like in Gecko/Blink. In any case, it would be good to make the spec require something more than "depends on user agent".

cc @nattokirai @litherum @svgeesus

[fantasai]

That's... interesting. No, the keyword inherit is not a conforming initial value. Cascade defines the initial value as being the same value the root element takes by default (as well as the value that non-inherited properties take by default). There's clearly some computed value on the root element: that value must be the “initial value” per CSS, and it must also be the value that's returned when the keyword initial is set, per the definition of initial. It's also worth noting that neither initial nor inherit can be specified values or computed values, they can only be cascaded values and the specified value becomes whatever those keywords represent. https://www.w3.org/TR/css-cascade-3/#defaulting

I think that makes this issue invalid, and WebKit has a bug.

In any case, it would be good to make the spec require something more than "depends on user agent".

I'm not aware of a need for the UAs to align on a particular font-family value, if you have one in mind I think you need to explain why it's needed in a separate bug? :)

[svgeesus]

Is Webkit treating body as the same as :root here? That is a bug.

As @fantasai says, there is no obvious value for the initial font-family that we could standardize on.

[zcorpan]

Is Webkit treating body as the same as :root here?

No. initial doesn't mean the value the root element has, rather the value it would have. So setting font-family on the root shouldn't have an effect on what initial keyword does.

Changing the test to style a div instead of body doesn't change the result in WebKit.

Anyway, if it is already well-defined that inherit can't be an initial value, then no need to change the spec.

WebKit bug: https://bugs.webkit.org/show_bug.cgi?id=200709

[zcorpan]

(The de facto initial value seems to be serif, but I don't think it's necessary to make it de jure.)