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Re: ::distributed and relative selectors (Was Re: [shadowdom]: Using :root to specify the insertion point in ::distributed)

From: Hayato Ito <hayato@google.com>
Date: Mon, 22 Apr 2013 15:36:48 +0900
Message-ID: <CAFpjS_3Mni7ta1+AH=dX3m7ctOSctjuc21+Fg+veKpHmRhGzjA@mail.gmail.com>
To: "Tab Atkins Jr." <jackalmage@gmail.com>
Cc: Dimitri Glazkov <dglazkov@google.com>, fantasai <fantasai.lists@inkedblade.net>, "www-style@w3.org" <www-style@w3.org>
On Fri, Apr 19, 2013 at 10:40 AM, Tab Atkins Jr. <jackalmage@gmail.com> wrote:
> On Thu, Apr 18, 2013 at 5:27 PM, Hayato Ito <hayato@google.com> wrote:
>> On Fri, Apr 19, 2013 at 2:44 AM, Tab Atkins Jr. <jackalmage@gmail.com> wrote:
>>> I think that, for the purpose of ::distributed, the scope element
>>> should be an abstract container, not the actual <content> element.
>>> This container would act as an element for the purposes of selectors,
>>> but it has no tagname or any other quality to select on.  So, #1, #2,
>>> and #3 would match, but #4 and #5 wouldn't, because the scoping
>>> element isn't named "content".
>>
>> I noticed that we don't need 4) and 5) to prove contradiction. See the
>> following example, introducing 4':
>>
>> 1). content::distributed(> .hello)               ->  Please assume this matches.
>> 2). content::distributed(:scope > .hello)        -> Matches. (1 and 2
>> should be equivalent according to the defintion of relative
>> selectors).
>> 3). content::distributed(*:scope > .hello)       -> Matches.
>> 4'). content::distributed(* > .hello)       -> Should not match.
>>
>> 3) matches, but 4') should not match.
>>
>> I think it is hard to justify using :scope in this context. I am
>> afraid that we should handle ':scope' in this context very *tricky* in
>> implementing this. Maybe the spec is wrong.
>> My proposal is using ':root' as suggested in the original thread.
> I don't understand how :root could help.  If :scope is problematic,
> presumably :root would have the same problems?

No, ':root' does not have a problem I mentioned. See the following example:

root-3). content::distributed(.hello:root)       -> Matches.
root-4'). content::distributed(.hello)       -> Matches

We don't have an inconsistency between root-3 and root-4' as seen in 3 and 4'.

> I don't have a problem with 4' matching, actually.  The virtual
> element must not show up in the selector's results, but that's all
> (and it can only appear if you use a selector like ":scope" or "*").
>
> ~TJ

Hmm. On the hat of implementors, 3 and 4') break the basic rule of
selectors. We need to have an extra hidden rule, virtual elements, to
explain its correctness both in the spec and implementations.
I am afraid that would make implementations unnecessary complex. If we
can have alternative way, like ':root', I'd prefer it to ':scope'.



--
Hayato
Received on Monday, 22 April 2013 06:37:35 UTC

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