[css3-selectors]: Proposal: :in-view() selector for better visibility control

Hi folks!

It would be perfect if we get the next pseudo class: :in-view() with a
different parameters
:in-view(all) - selected node is 100% visible in viewport
:in-view(partial) - selected node is partially visible in viewport
:in-view(none) - selected node is outside of viewport

And inverted logic using :not()
:not(:in-view(all)) - synonym of :in-view(none)
:not(:in-view(partial)) - selected node is partially INvisible in viewport
:not(:in-view(none)) - synonym of :in-view(all)

Real cases are the next.
If I have some absolutely positioned popup blocks inside of relative
positioned ones, sometimes it fall out from viewport due relative block
position I would like to return that block into a viewport again. Now I
have to use JS.

Other one is sticky behavior. I can hide something or change the position
just using :in-view(partial) selector. I don't need position: sticky
anymore :)

So, what do you think about it?

-- 
s0rr0w