protected void onMouseDown(final Context context, final Element parent, NativeEvent event,
final ValueUpdater<Integer> valueUpdater) {
Element target = Element.as(event.getEventTarget());
if (!getAppearance().getThumb(parent).isOrHasChild(target)) {
int value = getAppearance().getClickedValue(context, parent, new Point(event.getClientX(), event.getClientY()));
value = reverseValue(parent.<XElement> cast(), value);
value = normalizeValue(value);
valueUpdater.update(value);
return;
}