What about a sort of tag hierarchy in which the first level the tags would remain fixed, and in lower levels user-selected? Every post would only display the le

What about a sort of tag hierarchy in which the first level the tags would remain fixed, and in lower levels user-selected? Every post would only display the leaf tags of the branches to which it pertained, or something along that line. Well, I guess this would make search a bit harder to implement. Dunno, something that came up and I had to verbalize :)