code: def replace_tags(cls, raw_filter):
          
          for k, v in iter(cls.known_tags.items()):
              raw_filter = raw_filter.replace(k, v)
  
          return raw_filter
docs: Searches for known tags in the given string and replaces them with the
          corresponding regular expression.
  
          *raw_filter* is an (optionnaly tagged) regular expression.
  
          Returns the regular expression with known tags replaces by the
          corresponding regular expression.