code: def check_connection (self):
          
          if (self.parent_url is not None and
             not self.parent_url.startswith(u"file:")):
              msg = _("local files are only checked without parent URL or when the parent URL is also a file")
              raise LinkCheckerError(msg)
          if self.is_directory():
              self.set_result(_("directory"))
          else:
              url = fileutil.pathencode(self.url)
              self.url_connection = urlopen(url)
              self.check_case_sensitivity()
docs: Try to open the local file. Under NT systems the case sensitivity
          is checked.