docs: def ifinstalled(parser, token):
      """
      Old-style ``if`` tag that renders contents if the given app is
      installed. The main use case is:
  
      {% ifinstalled app_name %}
      {% include "app_name/template.html" %}
      {% endifinstalled %}
  
      so we need to manually pull out all tokens if the app isn't
      installed, since if we used a normal ``if`` tag with a False arg,
      the include tag will still try and find the template to include.
      """
      try:
          tag, app = token.split_contents()
      except ValueError:
          raise TemplateSyntaxError("ifinstalled should be in the form: "
                                    "{% ifinstalled app_name %}"
                                    "{% endifinstalled %}")
  
      end_tag = "end" + tag
      unmatched_end_tag = 1
      if app.strip("\"'") not in settings.INSTALLED_APPS:
          while unmatched_end_tag:
              token = parser.tokens.pop(0)
              if token.token_type == TOKEN_BLOCK:
                  block_name = token.contents.split()[0]
                  if block_name == tag:
                      unmatched_end_tag += 1
                  if block_name == end_tag:
                      unmatched_end_tag -= 1
          parser.tokens.insert(0, token)
      nodelist = parser.parse((end_tag,))
      parser.delete_first_token()
  
      class IfInstalledNode(Node):
          def render(self, context):
              return nodelist.render(context)
  
      return IfInstalledNode()