docs: def new_bootstrap_alert(visitor, block):
      """
      Format:
          
          {% alert class=error %}
          message
          {% endalert %}
      """
      if 'new' in block:
          txt = []
          cls = block['kwargs'].get('class', '')
          if cls:
              cls = 'alert-%s' % cls
          txt.append('<div class="alert %s">' % cls)
          if 'close' in block['kwargs']:
              txt.append('<button class="close" data-dismiss="alert">&times;</button>')
          text = visitor.parse_text(block['body'], 'article')
          txt.append(text)
          txt.append('</div>')
          return '\n'.join(txt)
      else:
          return bootstrap_alert(visitor, block)