[css-pseudo-4] Add discussion of properties from the originating element

[schenney-chromium]

Spec issue: #7591

Per resolution, properties not allowed on highlights but otherwise required to resolve units or modify colors are instead taken from the originating element.

[schenney-chromium]

Ping!

[fantasai]

Alright, question I'm not entirely clear on: what is the result of getComputedStyle() for font-size and border-width on the highlight pseudo given:

p { font-size: 20px; border-width: 10px; }
p::selection { font-size: 30px; border-width: 20px; }

?

[schenney-chromium]

Alright, question I'm not entirely clear on: what is the result of getComputedStyle() for font-size and border-width on the highlight pseudo given:

p { font-size: 20px; border-width: 10px; }
p::selection { font-size: 30px; border-width: 20px; }

?

Sorry I missed this way back. In any event. getComputedStyle in Chrome reports the originating element's font size because the font size in the selection pseudo is never applied and the font size is set from the originating element always.

<style> p { font-size: 20px; border-width: 10px; border-style: solid; border-color: green;} p::selection { font-size: 30px; border-width: 20px; border-style: solid; border-color: green;} </style>

Hello world

getComputedStyle(x, ":selection").fontSize

20px

The border properties are defaults, e.g. borderTopWidth > 0px.

[schenney-chromium]

I'd like to finally land this. I added the update for the custom property resolution.

[fantasai]

I think this text needs tweaking, since the language is a bit imprecise; but I think it'll be easier to tweak after merging so accepting it as-is for now.