code: def do_container(self, element, decl, pseudo):
          
          value = serialize(decl.value).strip()
  
          if '|' in value:
              namespace, tag = value.split('|', 1)
  
              try:
                  namespace = self.css_namespaces[namespace]
              except KeyError:
                  log(WARN, u'undefined namespace prefix: {}'.format(
                      namespace).encode('utf-8'))
                  value = tag
              else:
                  value = etree.QName(namespace, tag)
  
          step = self.state[self.state['current_step']]
          actions = step['actions']
          actions.append(('tag', value))
docs: Implement setting tag for new wrapper element.