function onElementMouseOver(e) {
    !shouldSilent(this, e)
        // "emphasis" event highlight has higher priority than mouse highlight.
        && !this.__highByOuter
        && traverseUpdate(this, singleEnterEmphasis);
}
@param {module:zrender/Element} el
@param {Function} [el.highDownOnUpdate] Called when state updated.
       Since `setHoverStyle` has the constraint that it must be called after
       all of the normal style updated, `highDownOnUpdate` is not needed to
       trigger if both `fromState` and `toState` is 'normal', and needed to
       trigger if both `fromState` and `toState` is 'emphasis', which enables
       to sync outside style settings to "emphasis" state.
       @this {string} This dispatcher `el`.
       @param {string} fromState Can be "normal" or "emphasis".
              `fromState` might equal to `toState`,
              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
       conveniently use hoverStyle when tap on touch screen without additional
       code for compatibility.
       But if the chart/component has select feature, which usually also use
       hoverStyle, there might be conflict between 'select-highlight' and
       'hover-highlight' especially when roam is enabled (see geo for example).
       In this case, `highDownSilentOnTouch` should be used to disable
       hover-highlight on touch device.
@param {boolean} [asDispatcher=true] If `false`, do not set as "highDownDispatcher".