'Value can be either a string in the format XX-XXXXXXXX-X or an
11-digit number.'

def clean(self, value):

    value = super(ARCUITField, self).clean(value)
    if (value in EMPTY_VALUES):
        return u''
    (value, cd) = self._canon(value)
    if (self._calc_cd(value) != cd):
        raise ValidationError(self.error_messages['checksum'])
    return self._format(value, cd)
