code: def render_head(self, ctx, data):
          
          req = inevow.IRequest(ctx)
          more = getattr(self.fragment, 'head', None)
          if more is not None:
              fragmentHead = more()
          else:
              fragmentHead = None
          return ctx.tag[filter(None, list(self.getHeadContent(req)) +
                                [fragmentHead])]
docs: This renderer calculates content for the <head> tag by concatenating the
          values from L{getHeadContent} and the overridden L{head} method.