code: def get_intern_pattern (self, url=None):
          
          if url is None:
              url = self.url
          if not url:
              return None
          if url.startswith('file://'):
              i = url.rindex('/')
              if i > 6:
                  # remove last filename to make directory internal
                  url = url[:i+1]
          return re.escape(url)
docs: Get pattern for intern URL matching.
  
          @return non-empty regex pattern or None
          @rtype String or None