code: function meshSetString (tiles) {
      return JSON.stringify(
          Object.entries(tiles).map(([,t]) => {
              return Object.entries(t.meshes).map(([,s]) => {
                  return s.map(m => m.created_at);
              });
          })
      );
  }
docs: Create a string representing the current set of meshes for a given set of tiles, based on their created timestamp. Used to determine when tiles should be re-collided.