W3C

Selectors Level 3 is a W3C Recommendation

The CSS Working Group has published Selectors Level 3 as a W3C Recommendation. Selectors are patterns that match against elements in a tree, and as such form one of several technologies that can be used to select nodes in an HTML or XML document. Selectors have been optimized for use with HTML and XML, and are designed to be usable in performance-critical code.