'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].'

def StringEscape(self, string, match, **_):

    if (self.current_expression.operator == 'regexp'):
        self.string += string.decode('string_escape')
    elif (match.group(1) in '\\\'"rnbt'):
        self.string += string.decode('string_escape')
    else:
        raise ParseError(('Invalid    escape    character    %s.' % string))
