docs: def totalNumberOfTiles(self, minZoom=None, maxZoom=None):
          "Return the total number of tiles for this instance extent"
          nbTiles = 0
          minZoom = minZoom or 0
          if maxZoom:
              maxZoom = maxZoom + 1
          else:
              maxZoom = len(self.RESOLUTIONS)
          for zoom in xrange(minZoom, maxZoom):
              nbTiles += self.numberOfTilesAtZoom(zoom)
          return nbTiles