'Validation
@param value: the value'

def __call__(self, value):

    other = self.other
    if ((current.request.env.request_method == 'POST') or (not other)):
        return (value, None)
    if (not isinstance(other, (list, tuple))):
        other = [other]
    for r in other:
        (value, error) = r(value)
        if error:
            return (value, error)
    return (value, None)
