render() {
    const attrsStr = Object.entries(this.attrs)
      .map(([k, v]) => ` ${k}="${escapeXml(v)}"`)
      .join('')
    if (this.content.length > 0) {
      const content = this.content
        .map(function (el) {
          if (typeof el.render === 'function') {
            return el.render()
          } else {
            return escapeXml(el)
          }
        })
        .join(' ')
      return stripXmlWhitespace(
        `<${this.name}${attrsStr}>${content}</${this.name}>`,
      )
    }
    return stripXmlWhitespace(`<${this.name}${attrsStr}/>`)
  }
Render the XML element to a string, applying appropriate escaping

@returns {string} String representation of the XML element