Custom element callbacks for builtins

[annevk]

I think in general web developers would appreciate having these callbacks available for normal elements too. See e.g., https://www.w3.org/Bugs/Public/show_bug.cgi?id=23250.

However, in that case they'd probably be in addition to what the browser already does internally for the element. That is not different from what is="" does though, so the proponents of that should be okay with this too.

[travisleithead]

I wonder if we could keep lifecycle callbacks for normal elements, but drop the declarative is= syntax? Would this mean that we wouldn't create custom constructors/prototypes as well? Seems like a lot of the auto-hookup feature of custom elements would be lost... but that might be OK?

[annevk]

We discussed at the F2F and decided not to do this. Was too complicated.