[cssom] [mediaqueries] Media query serialization doesn't work for newer spec features

[emilio]

I recently became confused because WebKit / Blink sorted the media features in media query lists, but @lilles did point out to me that https://drafts.csswg.org/cssom/#serialize-a-media-query does say that:

5. Sort the media features in lexicographical order.

But this has gone very out of date with newer mediaqueries features (like nested expressions, etc), which for now only Gecko supports. This also gets more interesting when we support the multi-value expression syntax in #2791...

Gecko has never implemented the sorting step, so I'd propose to drop it: we don't know of any compat issue due to that, it was just that I was looking at interop around MediaQueryList as a result of a Gecko bug. Also, Gecko's behavior is more intuitive to me but maybe I'm biased :)

If we don't drop it, we need to define how the sorting works for stuff like nested expressions and such. Basically, we'd need to define sorting among two arbitrary <media-condition>s.

Thoughts?

[lilles]

Drop sorting. I can't imagine anyone relying on non-interoperable re-ordering of media query expressions (famous last words).

Blink also currently removes duplicates, which isn't part of the algorithm, but is indicated by an example in the spec. We should remove that too.

[tabatkins]

Yup, we should just preserve the expression as-is.

I'll go fix the example that shows off deduplication.

[css-meeting-bot]

The CSS Working Group just discussed MQ serialization, and agreed to the following:

• RESOLVED: Do not sort or dedup MQs when serializing

The full IRC log of that discussion

<TabAtkins> Topic: MQ serialization
<astearns> github: https://github.com//issues/5627
<TabAtkins> astearns: Proposed resolution is to drop the CSSOM-specified sorting of MQs in lexicogrpahic order when serializing
<fantasai> TabAtkins: No objection, but one example shows removing duplicates as well
<fantasai> TabAtkins: Should also make sure that is covered as well
<TabAtkins> astearns: Consensus in the issue, looks like
<TabAtkins> emilio: Don't think Gecko has ever sorted, and we don't seem to have an issue
<TabAtkins> astearns: Did you dedup?
<TabAtkins> emilio: Don't think so; maybe as part of MQList apis, but not serialization. will doule-check
<TabAtkins> astearns: So any objections?
<TabAtkins> RESOLVED: Do not sort or dedup MQs when serializing