code: function(overlay) {
              var zIndex = Dom.getStyle(overlay.element, "zIndex");
              if (!isNaN(zIndex)) {
                  overlay.cfg.setProperty("zIndex", parseInt(zIndex, 10));
              } else {
                  overlay.cfg.setProperty("zIndex", 0);
              }
          }
docs: Ensures the zIndex configuration property on the managed overlay based instance
  is set to the computed zIndex value from the DOM (with "auto" translating to 0).
  
  @method _syncZIndex
  @param {Overlay} overlay The overlay instance being managed
  @protected