Re: Shadow tree style isolation primitive

> On Jan 12, 2015, at 2:07 PM, Brian Kardell <bkardell@gmail.com> wrote:
> On Mon, Jan 12, 2015 at 4:57 PM, Ryosuke Niwa <rniwa@apple.com <mailto:rniwa@apple.com>> wrote:
> 
> > On Jan 12, 2015, at 4:13 AM, chaals@yandex-team.ru <mailto:chaals@yandex-team.ru> wrote:
> >
> > 09.01.2015, 16:42, "Anne van Kesteren" <annevk@annevk.nl <mailto:annevk@annevk.nl>>:
> >> I'm wondering if it's feasible to provide developers with the
> >> primitive that the combination of Shadow DOM and CSS Scoping provides.
> >> Namely a way to isolate a subtree from selector matching (of document
> >> stylesheets, not necessarily user and user agent stylesheets) and
> >> requiring a special selector, such as >>>, to pierce through the
> >> boundary.
> >
> > Sounds like a reasonable, and perhaps feasible thing to do, but the obvious question is "why?"
> >
> > The use cases I can think of are to provide the sort of thing we do with BEM today. Is the effort worth it, or are there other things I didn't think of (quite likely, given I spent multiple seconds on the question)?
> 
> The benefit of this approach is that all the styling information will be in one place.  CSS cascading rules is already complicated, and having to consult the markup to know where the selector boundary is will be yet another cognitive stress.
> 
> - R. Niwa
> 
> 
> If it it necessary to reflect similar at the imperative end of things with qsa/find/closest (at minimum) - and I think it is the least surprising thing to do - then you've merely moved where the cognitive stress is, and in a really new way... Suddenly your CSS is affecting your understanding of the actual tree!  That seems.... bad.

I agree that having both style isolation and subtree isolation is desirable in some use cases such as Web app widgets.  However, there are other use cases for which style isolation without subtree isolation is desirable in non-App Web documents.

- R. Niwa