docs: function interfaceDescendantOf(interf1, interf2) {
          var x,
              parents = interf1[$interface].parents;
  
          for (x = parents.length - 1; x >= 0; x -= 1) {
              if (parents[x] === interf2) {
                  return true;
              }
              if (interfaceDescendantOf(interf1, parents[x])) {
                  return true;
              }
          }
  
          return false;
      }