function __construct($attributes = nil)
{
parent::__construct($attributes);
// ensure that a default range is set
if (is_null($this->range)) {
$this->set_range(array("1970-01-01", date('Y-m-d')));
}
if (is_null($this->default)) {
$this->set_default(array("1970-01-01", date('Y-m-d')));
}
}
