On Thu, Sep 19, 2013 at 4:09 PM, Tab Atkins Jr. jackalm...@gmail.com wrote:
So, to be clearer, we'd be adding two new combinators, ^ and ^^.
^, the shadow combinator (or hat), pierces the upper-boundary
encapsulation of a shadow root. The LHS has to be a component,
something with an actual shadow root. ^^, the all shadows
combinator (or cat, or double-hat), is identical, but it pierces
*all* shadow root upper boundaries.
Further use-case exploration by the Polymer folk has revealed that
this definition of ^^ is a bit too weak for a lot of reasonable
use-cases.
One of the major uses of ^^ is to simply target all x-foo elements
for styling. Unfortunately, this means you need to ugly up your
selectors:
x-foo + div.bar, * ^^ x-foo + div.bar {...}
As far as they could tell from use-case exploration, this is by far a
more common use than what's implied by the stricter form defined in
the quote above.
To fix this, we propose that ^^ should instead be interpreted as
simply a more powerful descendant selector. Writing * ^^ x-foo
will selector *all* x-foo elements within your context, or in lower
contexts. (It'll miss the root element if it's an x-foo, but that's
probably rare, and you can catch it by just writing a selector like
what I wrote above.)
Related to this, we have to figure out what the relative strength of
selectors are in different trees. Again, according to use-case
exploration, it seems that styling *inside* a component is basically
always setting *defaults*, which should be overrideable by the outside
world. To address this in a reliable way, I propose adding another
Cascade layer
http://dev.w3.org/csswg/css-cascade/#cascadinghttp://dev.w3.org/csswg/css-cascade/#cascading,
between Origin and Scope, which is Tree-of-Trees position. Higher
trees (closer to the document root) beat lower trees. Sibling trees
(which can happen when a single element has multiple shadow roots
attached) are youngest-beats-oldest.
(I had thought to handle this with my proposal for setting styles to a
default origin, but it doesn't quite mesh. My !default idea makes
a style which loses to *everything* non-default, including
inheritance. The Polymer people didn't want things *this* weak.)
~TJ
