W3C home > Mailing lists > Public > www-style@w3.org > February 2014

Re: Shadow DOM Encapsulation

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Thu, 6 Feb 2014 19:02:00 -0800
Message-ID: <CAAWBYDCLhrnBjKv8KpEBEpnDrzH8hdVexJvJyBRrGdQweczi5g@mail.gmail.com>
To: Peter Linss <peter.linss@hp.com>
Cc: www-style list <www-style@w3.org>
On Thu, Feb 6, 2014 at 6:54 PM, Peter Linss <peter.linss@hp.com> wrote:
> On Feb 6, 2014, at 5:23 PM, Tab Atkins Jr. <jackalmage@gmail.com>
>  wrote:
>> Note also that this isn't quite as easy as it sounds.  When you expose
>> things, where are they relative to everything else?
>
> They are in the same place as they are defined, the structure is preserved for everything exported.
>
> For example, given the shadow DOM:
> <component>
>   <part-one export>
>     <sub-part-one />
>   </part-one>
>   <part-two>
>     <sub-part-two export>
>       <sub-sub-part-two />
>     </sub-part-two>
>   </part-two>
> </component>
>
> You'd see it as though it were defined as:
> <part-one>
>   <sub-part-one />
> </part-one>
> <sub-part-two>
>   <sub-sub-part-two />
> </sub-part-two>

Oof, so then "part-one + sub-part-two" would actually match?  That's
seems super weird to me.

>>> The other part of my proposal was to simply use pseudo-elements to directly select the exported component pieces by name, and to relax the restrictions on pseudo-element selectors to allow pseudo-classes, attribute selectors, and descendants (with combinators).
>>>
>>> With those restrictions relaxed, it's not necessary to flatten the pseudo-element space, so the internal structure of exported pieces could be maintained.
>>>
>>> So a piece could be selected as:
>>> component ::piece { ... }
>>> it's child could be selected as:
>>> component ::piece ::child-peice { ... }
>>> etc, with the full expressiveness of selectors. This addresses your points #2 & #3.
>>
>> Well, no, not quite.  You're using spaces where they're not allowing.
>> It'd have to be at least:
>>
>>  component::piece::child-piece
>>
>> Or something else for the child-piece part that allowed combinators.
>
> No, I really meant spaces, i.e. descendant combinators (see "loosening restrictions on use of pseudo-element selectors" in a previous message). You could use other combinators as needed to address specific nodes. There's no magic pseudo-element or combinator needed to pierce the shadow layer, the shadow component simply exports its parts as a structure of pseudo-elements.

That completely changes the meaning of pseudo-elements, though.
That's what I'm trying to allude to.

"component ::before" explicitly means the same thing as "component
*::before".  Similarly, "component ::piece" would mean the same thing
as "component *::piece", which is definitely not what you're
intending.  This is part of the definition of pseudo-element syntax; I
don't think it's reasonable to change it.

> The only interesting thing here is that there's an implied > between all pseudo-elements and the rest of the selector, so:
> p::first-line
> is morally equivalent to:
> p > ::first-line
> That's the way Gecko at-least used to do it internally...
>
> We did this back in '98 or so in Gecko when building form controls out of "anonymous" boxes and hidden dom nodes (for content and event handling), essentially the 16 year-old precursor to today's shadow-dom. The interesting "anonymous" boxes each had a pseudo-element name and you could simply style them with normal CSS selectors.

Are you implying then that the ::piece thing is *actually* a child (or
descendant) of the element in the normal way we use the term, but is
only matchable via its special name?  That's pretty weird, I think.

> I accept the symmetry argument between the structure exposed to selectors and the JS APIs, but this isn't the right place to debate the JS APIs.

Right, but given the JS APIs, it's the right place to make arguments
about matching them. ^_^

~TJ
Received on Friday, 7 February 2014 03:02:47 UTC

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