[whatwg] scoped style sheets and @-rules

[L. David Baron]

I thought I'd brought this issue up before, but I can't seem to find
a record of it.

http://www.whatwg.org/specs/web-apps/current-work/multipage/semantics.html#attr-style-scoped
currently says that, inside scoped style sheets, @page rules are
ignored, but other @-rules are honored, scoped either to the style
sheet or to the subtree.

I think it makes perfect sense to honor @-rules whose effects are
scoped to the style sheet (@namespace, also @charset if it weren't
already ignored) or @-rules whose effects are to condition the rules
inside of them (all the rules in css3-conditional: @media,
@supports) or import more rules (@import).

But I think it's a large amount of extra implementation complexity
to honor @-rules whose purpose is to build global dictionaries (in
particular, @keyframes and @font-face), and I suspect the end result
of honoring them would yield technology that's more confusing for
authors.  Anything that can be done by changing the meaning of an
@keyframes or @font-face rule within a subtree could also be done by
declaring a different animation rule or font-family within that
subtree.  I suspect the extra clarity from the latter makes it a
better authoring practice anyway, so I don't think implementations
should be required to add support for a feature that it's better to
not use.

Thus I think the specification should mandate that @keyframes and
@font-face are ignored in scoped style sheets, just like @page.

I think it would also be good if the specification left the effects
of unknown @-rules undefined until whether they should be supported
can be properly considered.

-David

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                           http://www.mozilla.org/   𝄂