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Re: [css-scoping] Was shadow host intended to be more feature-less than "featureless"?

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Tue, 7 Apr 2015 17:48:52 -0700
Message-ID: <CAAWBYDAKw-ZKQ9Dwbo2P_Y44pnD2SO7nEDc5uQU1cXWOa79ugA@mail.gmail.com>
To: "L. David Baron" <dbaron@dbaron.org>
Cc: www-style list <www-style@w3.org>
On Tue, Apr 7, 2015 at 4:59 PM, L. David Baron <dbaron@dbaron.org> wrote:
> On Tuesday 2015-04-07 16:45 -0700, Tab Atkins Jr. wrote:
>> Ugh, hit send a little too early.
>>
>> On Tue, Apr 7, 2015 at 4:43 PM, Tab Atkins Jr. <jackalmage@gmail.com> wrote:
>> > Correct, it *should* match those pseudos.  The whole "featureless"
>> > concept exists *solely* to prevent a component author from
>> > *accidentally* matching the host element due to the component *user*
>> > doing something to it.  The component author should be able to write a
>> > rule against a `.foo` class without risking accidentally targeting the
>> > host element just because the component user, unaware that .foo is
>> > being used inside the component, puts a class=foo on the host element
>> > for their own unrelated styling purposes.
>>
>> Note, though, that the Blink implementation currently *does* exclude
>> everything - it literally returns false immediately if the selector
>> has anything else in it.  This was semi-intentional when implemented,
>> but I defined things the way I did on purpose, and Blink's current
>> behavior is a bug.
>
> But Blink's behavior seems like a much clearer mental model for
> authors:  that only :host, :host(), and :host-context() can match
> outside of the component.
>
> It seems odd to me that when the host element is a p element
> currently in the :active state, that the following selectors would
> match it (as part of a larger selector with combinators):
>   :host
>   :host(p)
>   :host(:hover)
>   :active
> but that the following:
>   p
> would not match.

Hm, for some reason I'd forgotten about :host().  I suppose
:host(:hover) isn't any more difficult than :host:hover.  I guess I'd
be okay with redefining featureless elements more strictly to make
them not match *any* selectors unless otherwise specified?

> And if :active on the host element works, why shouldn't authors
> expect it to also work on ancestors of the host element (which
> doesn't work, since those ancestors aren't considered at all)?

Ancestors aren't part of the shadow tree at all; I'm not sure why
authors would expect them to be matched in the first place, as that
would violate the entire point of the shadow tree.  The host element
is the only one that's kinda ambiguous about whether a component
should be able to match it or not.

~TJ
Received on Wednesday, 8 April 2015 00:49:39 UTC

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