[webkit-dev] Multiple inheritance in the DOM

Adam Barth abarth at webkit.org
Thu Jul 26 15:15:29 PDT 2012

On Thu, Jul 26, 2012 at 2:58 PM, Alan Stearns <stearns at adobe.com> wrote:

> On 7/26/12 2:36 PM, "Adam Barth" <abarth at webkit.org> wrote:
> >
> >On Thu, Jul 26, 2012 at 2:29 PM, Alexandru Chiculita <achicu at adobe.com>
> >wrote:
> >
> >I don't see any advantage in having the interface anyway, so why don't we
> >just it let be a separate object and add two helper methods instead. I
> >can only imagine that other browsers might have the same issue anyway.
> >
> >document.getRegionForElement(element)
> >-> where element can be both Element and CSSPseudoElement
> >-> this may return null in case of no region being associated, so there's
> >no need for instanceof tricks anymore.
> >
> >region.element
> >-> that can return either Element or CSSPseudoElement
> >
> >BTW, is there any base class shared across Element and CSSPseudoElement?
> >
> >
> >Greping for CSSPseudoElement in WebCore appears to return zero results.
> >
> >
> >Discussing this issue with Sam in #webkit, we wondered whether another
> >solution is to not implement the CSSOM for Regions.  Is there are strong
> >use case for having this CSSOM in the first place?
> >
> >
> >Adam
> CSSPseudoElement is something I want to bring up soon in the CSS WG.
> Future extensions like this as to what can become a CSS Region is the
> motivation for separating out the Region interface. Whether there's a
> shared base class that makes sense is still to be determined.
> There are strong use cases for the object model for CSS Regions. Adobe has
> projects we'd like to base on CSS Regions, and script access  will be
> vital for these efforts. We've also been building prototypes of other CSS
> extensions using the CSS Regions OM. I understand that there are projects
> based on IE10's version of CSS Regions where script access is required.
> And in general I'd rather avoid adding new things to the platform that are
> opaque to scripting.

That all seems very vague.  Can you explain what you have in mind?

> For Alex's suggestion above, would there be any problems with a parameter
> (for the first method) and return type (for the second) that could be an
> Element or something else? Adding two helper methods seems messier to me
> than what's currently specced, but I'm open to the idea if it's much
> easier to implement.

It depends on how many things will implement Region.  If there are N
things, you'll need to add N properties and you're essentially asking web
developers to call QueryInterface on the object to see what sort of Region
it really is.

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