I can define a hierarchical Tag

(User Story, Investigate , Priority: High, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Tag Sets
Summary: This used to work, but got broken along the line. Get it working again, and create some improved UI for it.
A hierarchical Tag is, in principle, simply a Tag with slashes in the name. The interesting part will come in the associated Stories for UI and grouping.