Pseudo-classes - CSS: Cascading Style Sheets
index of standard pseudo-classes :active :any-link :blank :checked :current :default :defined :dir() :disabled :drop :empty :enabled :first :first-child :first-of-type :fullscreen :future :focus :focus-visible :focus-within :has() :host :host() :host-context() :hover :indeterminate :in-range :invalid :is() :lang() :last-child :last-of-type :left :link :local-link :not() :nth-child() :nth-col() :nth-last-child() :nth-last-col() :nth-last-of-type() :nth-of-type(...
... selectors level 4 working draft defined :any-link, :blank, :local-link, :scope, :drop, :current, :past, :future, :placeholder-shown, :user-invalid, :nth-col(), :nth-last-col(), :is() and :where().

Interfacing with the XPCOM cycle collector
//if your class is a wrapper cache: //ns_impl_cycle_collection_unlink_preserved_wrapper tmp->msomeobj = nullptr; ns_impl_cycle_collection_unlink_end in the destructor, you should call mozilla::dropjsobjects(this); in your traverse method you need to list members involved in the cycle collector, i-e no js objects: ns_impl_cycle_collection_traverse_begin(nsfoo) ...