...probably? I suppose? There doesn't seem to be a way to set the multiple values of a mapping in one call.  This brings up an issue with the param handling: what should we do about `/foo;a=1;a=2,3,4/` ? is `a` 1? or [2,3,4]? or [1,2,3,4] ? or [1, [2,3,4]] ? and if it's [2,3,4], is params['a'] = 4? or [2,3,4] ? Yay semantics!