code: function(node) {
          var zIndex = node._style.graphicZIndex;
          
          // Everything must have a zIndex. If none is specified,
          // this means the user *must* (hint: assumption) want this
          // node to succomb to drawing order. To enforce drawing order
          // over all indexing methods, we'll create a new z-index that's
          // greater than any currently in the indexer.
          if (zIndex == null) {
              zIndex = this.maxZIndex;
              node._style.graphicZIndex = zIndex; 
          } else if (zIndex > this.maxZIndex) {
              this.maxZIndex = zIndex;
          }
      }
docs: Method: determineZIndex
  Determine the z-index for the current node if there isn't one,
  and set the maximum value if we've found a new maximum.
  
  Parameters:
  node - {DOMElement}