toSvg(attrs = {}) {
    const combinedAttrs = {
      ...this.attrs,
      ...attrs,
      ...{ class: classnames(this.attrs.class, attrs.class) },
    };

    return `<svg ${attrsToString(combinedAttrs)}>${this.contents}</svg>`;
  }
Create an SVG string.
@param {Object} attrs
@returns {string}