function isHighDownDispatcher(el) {
    return !!(el && el.__highDownDispatcher);
}
Set basic textStyle properties.
See more info in `setTextStyleCommon`.
@param {Object|module:zrender/graphic/Style} textStyle
@param {module:echarts/model/Model} model
@param {Object} [specifiedTextStyle] Can be overrided by settings in model.
@param {Object} [opt] See `opt` of `setTextStyleCommon`.
@param {boolean} [isEmphasis]