Globally disambiguate epub vs html element definitions

[jyasskin]

EPUB defines <audio> and <link> elements that conflict with the HTML definitions. Specifications that need to refer to these elements can use a link-defaults block to do so, but it would be nice to find a way to mark specs as "targeting web browsers" or similar that would act as a more global and reliable set of defaults.

Respec has the "profiles" feature that does something similar, but with a much smaller set of specifications than I think we'd want here.

browser-specs has the categories field with a "browser" value that might work well.

[tabatkins]

Yeah, there's a few more elements they conflict on as well, like body. Dealing with this is... interesting tho.

browser-specs's "categories" field is potentially interesting, but while it's still just a single value it's of limited use. I guess it would still be useful to restrict yourself to "browser" entries, which would exclude epub specs, presumably. (Confirmed, it does.)

Hmmmm, yeah, this sounds reasonable.

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Two design questions, then, which are linked:

1. What's the default? "all" or "browser"?
2. What's the exact effect? Drops refs entirely if they're from specs that aren't in the specified sets, or just make them auto-lose when both preferred and non-preferred categories are present in the possible refs?

Like, say I defaulted to "browser". Should the epub specs be required to specify "all" to cross-link to each other, or should it be okay for them to cross-link as long as it's not ambiguous? If I allow the latter, it means they might link to each other naively (since it works when the terms are unique) and then accidentally link to HTML's <audio> since they're defaulted to "browser". Maybe I can log a warning if your ref resolves to a spec not in the specified category, similar to what I do for unexported terms, so you can either change the linking category or specify the spec shortname with the link to let Bikeshed know that you understand what you're doing (like you can do to link to unexported terms).

Maybe I need some notion of preference strength. Hmm. This'll require some thought.

[tidoust]

HTML vs. EPUB is the main case that creates duplication but note w3c/webref#1337 lists a few additional cases where elements are defined in more than one spec.