Tweak

src/util/graphic.js

@@ -516,6 +516,14 @@ export function setHoverStyle(el, hoverStyle) {
  *               for example, when this method is called when `el` is
  *               on "emphasis" state.
  *        @param {string} toState Can be "normal" or "emphasis".
+ *
+ *        FIXME
+ *        CAUTION: Do not expose `highDownOnUpdate` outside echarts.
+ *        Because it is not a complete solution. The update
+ *        listener should not have been mount in element,
+ *        and the normal/emphasis state should not have
+ *        mantained on elements.
+ *
  * @param {boolean} [el.highDownSilentOnTouch=false]
  *        In touch device, mouseover event will be trigger on touchstart event
  *        (see module:zrender/dom/HandlerProxy). By this mechanism, we can