code: private void startSliding(boolean highlight, boolean fireEvent) {
  		if (highlight) {
  			DOM.setElementProperty(lineElement, "className", SLIDER_LINE + " "
  					+ SLIDER_LINE_SLIDING);
  			DOM.setElementProperty(knobImage.getElement(), "className", SLIDER_KNOB + " "
  					+ SLIDER_KNOB_SLIDING);
  		}
  	}
docs: Start sliding the knob.
  
  @param highlight
  true to change the style
  @param fireEvent
  true to fire the event