function ff_integer_or_empty(element, message)
{
    if (element.value != '') {
        var ex  = /(^-?\d\d*$)/;
        if (!ex.test(element.value)) {
            if (message=='') message = element.name+" must be integer.\n";
            ff_validationFocus(element.name);
            return message;
        } // if
    } // if
    return '';
} // ff_integer_or_empty