docs: function(x, y, w, h) {
          var rect,
              mbr = this._mbr || this;
          if (typeof x === "object") {
              rect = x;
          } else {
              rect = {
                  _x: x,
                  _y: y,
                  _w: w,
                  _h: h
              };
          }
  
          return (
              rect._x >= mbr._x &&
              rect._x + rect._w <= mbr._x + mbr._w &&
              rect._y >= mbr._y &&
              rect._y + rect._h <= mbr._y + mbr._h
          );
      }