[css-cascade-6] Support @import scope() syntax

[andruud]

#7348

[andruud]

Note that this PR has two commits. The first commit copies over the @import section from level 5, verbatim.

[cdoublev]

- [ scope( [ (<<scope-start>>) ]? [ to (<<scope-end>>) ]? | <<scope-start>> ) ]
+ [ scope( [ [ (<<scope-start>>) ]? [ to (<<scope-end>>) ]? ]! | <<scope-start>> ) ]

(do not allow empty alternative)

[andruud]

But @import scope() is valid, though. It gives you an "implicit scope", i.e. equivalent to @scope { }.

[cdoublev]

Ok, that is intentional then. Sorry! =)

[romainmenke]

Shouldn't this then be @import scope in parallel with @import layer?

I'd rather not have authors needing to remember:

valid	invalid
@import layer	@import layer()
@import scope()	@import scope

[andruud]

@romainmenke Ah, yes, that's seems better.

[cdoublev]

Is it possible to edit Cascade 4 and 5 to prevent w3c/reffy from extracting <import-conditions>, which would be removed by this PR in Cascade 6?

- @import [ <url> | <string> ] ... <import-conditions> ;
- <import-conditions> = [ supports( [ <supports-condition> | <declaration> ] ) ]? <media-query-list>?
+ @import [ <url> | <string> ] ... [ supports( [ <supports-condition> | <declaration> ] ) ]? <media-query-list>? ;

---

Is it possible to define <supports()> and <media()> in Conditional 5, and <scope()> in Cascade 6, to avoid duplicate/overlapping definitions?

For example, supports() is defined differently in CSS Values 5, Conditional 5, Cascade 4/5.

<supports()>, <media()>, <media-query-list>, would define the import conditions.

@import [ <url> | <string> ]
        [[ layer | layer(<layer-name>) ] || <scope()> || <supports()> || <media()>]?
        <media-query-list> ;

<scope()> = scope( [ <scope-selector> | <scope-start> ]? )
<supports()> = supports( [ <supports-condition> | <declaration> ] )
<media()> = media( <media-query-list> )

Note: <media-query-list> does not need ? as it implicitly accepts an empty list.

<scope-selector> would be defined below the definition of @scope with @scope <scope-selector>? { ... }.

At least, the grouping brackets no longer seem necessary around scope(), now that it is implicitly optional.

[andruud]

@cdoublev That does sound quite reasonable, but I'll wait for an editor to have an opinion on what this should look like.

<media()> would be spec'ed later / separately, since we don't have a resolution to add it yet.

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Trying another editor, since @mirisuzanne is unresponsive.