The location class relates to links, both visible to the document and metadata:
:linkmatches unvisited links.
:visitedmatches visited links.
:local-linkmatches links whose absolute URL is the same as the document's, e.g. for anchors on the same page.
:targetmatches elements with the target of the document URL.
:target, but also elements with a descendent which is the target of the document URL.
:scopematches any element which is a reference point for selectors to match against.