code: function Definable(
      zrId,
      svgRoot,
      tagNames,
      markLabel,
      domName
  ) {
      this._zrId = zrId;
      this._svgRoot = svgRoot;
      this._tagNames = typeof tagNames === 'string' ? [tagNames] : tagNames;
      this._markLabel = markLabel;
      this._domName = domName || '_dom';
  
      this.nextId = 0;
  }
docs: Manages elements that can be defined in <defs> in SVG,
  e.g., gradients, clip path, etc.
  
  @class
  @param {number}          zrId      zrender instance id
  @param {SVGElement}      svgRoot   root of SVG document
  @param {string|string[]} tagNames  possible tag names
  @param {string}          markLabel label name to make if the element
  is used