Accrues digits and the plus sign to
        _accrued_input_without_formatting for later use. If next_char contains
        a digit in non-ASCII format (e.g. the full-width version of digits),
        it is first normalized to the ASCII version. The return value is
        next_char itself, or its normalized version, if next_char is a digit
        in non-ASCII format. This method assumes its input is either a digit
        or the plus sign.

def _normalize_and_accrue_digits_and_plus_sign(self, next_char, remember_position):
        """Accrues digits and the plus sign to
        _accrued_input_without_formatting for later use. If next_char contains
        a digit in non-ASCII format (e.g. the full-width version of digits),
        it is first normalized to the ASCII version. The return value is
        next_char itself, or its normalized version, if next_char is a digit
        in non-ASCII format. This method assumes its input is either a digit
        or the plus sign."""
        if next_char == _PLUS_SIGN:
            normalized_char = next_char
            self._accrued_input_without_formatting += next_char
        else:
            next_digit = unicode_digit(next_char, -1)
            if next_digit != -1:
                normalized_char = unicod(next_digit)
            else:  # pragma no cover
                normalized_char = next_char
            self._accrued_input_without_formatting += normalized_char
            self._national_number += normalized_char
        if remember_position:
            self._position_to_remember = len(self._accrued_input_without_formatting)
        return normalized_char