code: def StringEscape(self, string, match, **_):
      
      precondition.AssertType(string, Text)
  
      # Allow unfiltered strings for regexp operations so that escaped special
      # characters (e.g. \*) or special sequences (e.g. \w) can be used in
      # objectfilter.
      if self.current_expression.operator == "regexp":
        self.string += compatibility.UnescapeString(string)
      elif match.group(1) in "\\'\"rnbt":
        self.string += compatibility.UnescapeString(string)
      else:
        raise ParseError("Invalid escape character %s." % string)
docs: Escape backslashes found inside a string quote.
  
      Backslashes followed by anything other than [\'"rnbt] will raise an Error.
  
      Args:
        string: The string that matched.
        match: The match object (m.group(1) is the escaped code)
  
      Raises:
        ParseError: For strings other than those used to define a regexp, raise an
          error if the escaped string is not one of [\'"rnbt].