Use CSSOMString where appropriate

[zcorpan]

See w3c/csswg-drafts#1266

I think all media attributes as well as img/source sizes should be CSSOMStrings since they use CSS syntax.

cc @SimonSapin

[SimonSapin]

Probably anything that goes trough https://drafts.csswg.org/css-syntax/#tokenization … except I suppose text nodes that happen to be in a <style> element. Stylo also does replacement (of surrogates to U+FFFD) there when parsing a stylesheet, but I don’t think that case can be as neatly expressed though use of CSSOMString.

[annevk]

Does the CSS parser have entry points yet for code points or scalar values?

[SimonSapin]

https://drafts.csswg.org/css-syntax/#input-byte-stream

When parsing a stylesheet, the stream of Unicode code points that comprises the input to the tokenization stage might be initially seen by the user agent as a stream of bytes

Might, not necessarily.

To decode the stream of bytes into a stream of code points, UAs must use the decode algorithm defined in [ENCODING], with the fallback encoding determined as follows.

Code points, even though decode emits scalar values. I think this implicit “upcasting” is fine.

https://drafts.csswg.org/css-syntax/#input-preprocessing

The input stream consists of the code points pushed into it as the input byte stream is decoded.

This is the other entry point. The wording should be tweaked so that it doesn’t imply that these code point necessarily come directly from decoding a byte stream. CC @tabatkins

[annevk]

"Might" seems rather bad. Can't we just have an explicit entry point for bytes and one for code points? (And yes, as defined a scalar value is a code point: https://infra.spec.whatwg.org/#scalar-value.)