code: def check(self, url_data):
          
          headers = []
          for name, value in url_data.headers.items():
              if name.startswith(self.prefixes):
                  headers.append(name)
          if headers:
              items = [u"%s=%s" % (name.capitalize(), url_data.headers[name]) for name in headers]
              info = u"HTTP headers %s" % u", ".join(items)
              url_data.add_info(info)
docs: Check content for invalid anchors.