code: function (child) {
              var childIndex = this.getChildIndex(child);
              if (childIndex >= 0 && childIndex < (this.children.length - 1)) {
                  // note : we use an inverted loop
                  this.children.splice((this.children.length - 1), 0, this.children.splice(childIndex, 1)[0]);
                  // increment our child z value based on the next child depth
                  child.pos.z = this.children[(this.children.length - 2)].pos.z - 1;
              }
          }
docs: Move the specified child the bottom (z depth).
  @name moveToBottom
  @memberOf me.Container.prototype
  @function
  @param {me.Renderable} child