> On Apr 27, 2015, at 9:50 PM, Hayato Ito <hay...@chromium.org> wrote:
> The feature of "<shadow> as function" supports *subclassing*. That's exactly 
> the motivation I've introduced it once in the spec (and implemented it in 
> blink). I think Jan Miksovsky, co-author of Apple's proposal, knows well that.

We're (and consequently I'm) fully aware of that feature/prosal, and we still 
don't think it adequately addresses the needs of subclassing.

The problem with "<shadow> as function" is that the superclass implicitly 
selects nodes based on a CSS selector so unless the nodes a subclass wants to 
insert matches exactly what the author of superclass considered, the subclass 
won't be able to override it. e.g. if the superclass had an insertion point 
with select="input.foo", then it's not possible for a subclass to then override 
it with, for example, an input element wrapped in a span.

> The reason I reverted it from the spec (and the blink), [1], is a technical 
> difficulty to implement, though I've not proved that it's impossible to 
> implement.

I'm not even arguing about the implementation difficulty. I'm saying that the 
semantics is inadequate for subclassing.

- R. Niwa

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