A Journey Through The History Of CSS, Mathematics, And CS To Find Out! In my quest to find out why we call tags “tags” I learned about mathematician Emil Post (1897-1954), complexity theory, the children’s game of “tag”, the DOM as a tree & why we call them CSS “rules” (it has to do with cellular automata!) In this talk we’ll walk through the many rabbit holes I went down trying to answer this question & learn just how tied the modern browser is to fundamental computer science.