> 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