attributeChangedCallback(name, old, val) {
    if (this.ready && old !== val) {
      switch (name) {
        case 'body-class':
          this.root.querySelector('.markdown-body')?.setAttribute('class', this.bodyClass)
          break
        case 'src':
          if (this.auto) this.render()
      }
    }
  }
@param {string} name
@param {string} old
@param {string} val