Thread:Talk:Requests for comment/Scoping site CSS/Performance impact/reply (2)

Descending selectors are already widely used in MediaWiki in its existing skins. I don't see the point about performance (yes there was a performance issue, but now that MediaWiki has decided to use HTML5 as the default, this already implies a decent implementation of CSS and fast selectors. Every HTML5 renderer already has a decent speed for descending selectors. The issues are generally elsewhere, in unexpected defects of the rendering (e.g. in the box model, or rules of inheritance, or placement problems in case of conflicting restriction rules such as width vs. left and right, centering and effect of margins)