[css-syntax] <stylesheet> grammar construct should be named differently since it's not a "style sheet"

[jyasskin]

As discussed in #5697 (comment), "@import rules must precede all other valid at-rules and style rules in a style sheet" ([css-cascade]), but that's not the same "style sheet" as is spelled "<stylesheet>" and appears inside things like the conditional at-rules. This isn't a terrible problem, but it's also a bit confusing.

@fantasai suggested the right fix is to rename <stylesheet>. The telecon discussion suggested to explicitly ask @tabatkins if they object.

[tabatkins]

I don't object, just not sure what new name to use, since <stylesheet> means "anything allowed in a stylesheet (except those are only allowed in a top-level context, like @import)".

[svgeesus]

<stylesheet-body> perhaps, and the part where @import etc live could be <stylesheet-head> and thus, a stylesheet is <stylesheet-head> <stylesheet-body>

[fantasai]

I was going to suggest <styleset> but @svgeesus’s suggestion is a nice idea. Do we allow @font-face and @Keyframes inside conditional rules yet, though? Because if not then there's a top-level vs. encased distinction rather than a header vs. body distinction.

[tabatkins]

After discussing with @fantasai we decided that <stylesheet-body> makes the most sense, even if we don't use any sort of *-head production. (I'm just personally not a fan of "styleset".)

We'll defer actually making the change until January, since virtually all of the specs currently using it are pending publication currently, and will go up before a new Syntax /TR will. We'll just do some editorial repubs for all of them later once Syntax gets republished.

[tabatkins]

I ended up making this moot with the new Syntax text, since I changed all the productions anyway. Nothing is named <stylesheet> anymore. (Things that previously used it now just use <rule-list>.)