code: function (pageX, pageY) {
          
              var height = this.element.offsetHeight,
                  mousePoint = new YAHOO.util.Point(pageX, pageY),
                  elementRegion = Dom.getRegion(this.element);
          
              elementRegion.top -= 5;
              elementRegion.left -= 5;
              elementRegion.right += 5;
              elementRegion.bottom += 5;
          
              this.logger.log("context " + elementRegion, "ttip");
              this.logger.log("mouse " + mousePoint, "ttip");
          
              if (elementRegion.contains(mousePoint)) {
                  this.logger.log("OVERLAP", "warn");
                  this.cfg.setProperty("y", (pageY - height - 5));
              }
          }
docs: Fired when the Tooltip is moved, this event handler is used to
  prevent the Tooltip from overlapping with its context element.
  @method preventOverlay
  @param {Number} pageX The x coordinate position of the mouse pointer
  @param {Number} pageY The y coordinate position of the mouse pointer