Re: The :min-width/:max-width pseudo-classes

On 3/22/13 1:25 PM, Tab Atkins Jr. wrote:
> No, the problem is that a layout manager needs to be invoked at all to
> resolve selectors.  If an internal API wants up-to-date styles but
> doesn't actually care about layout, right now it can do that by just
> resolving all the selectors and running the cascade.  With the
> introduction of viewport-element-relative pseudoclasses, it needs to
> resolve layout, at least partially.

So I actually have a question.

What determines whether something is a "viewport"?  I seem to have 
missed that somewhere in here.

In the <iframe> case it's simple: it's the (immutable!) 
namespace+localName of the element.  But in the case we're talking about?

-Boris