Parse an identifier and return it (possibly an empty string).
        Updates ``pos``.

def _parse_ident(self):
        """Parse an identifier and return it (possibly an empty string).
        Updates ``pos``.
        """
        remainder = self.string[self.pos:]
        ident = re.match(r'\w*', remainder).group(0)
        self.pos += len(ident)
        return ident