Restrict selector matching to only match up to (and including) the scoping element, but not its ancestors.
Note: Will wait with uploading the patch until 73190 settles.
Created attachment 118541 [details]
patch (requires 67790, 73190), with flag
New Year request for review! :)
Created attachment 124899 [details]
Updated patch after landing basic <style scoped> implementation. Remarks: I'm storing the scope to use in member variables in order to reduce the amount of paramter passing and #ifdef-ing. I'm not sure if I should go further and do this for fastCheckSingleSelector as well (although this would require making that template function a class member) or, conversely, whether it's a good idea in the first place.
Splitting this up into several patches as discussed with Antti on IRC.