1. Add behavior to ActiveRecord

[
	'class' => 'ant\category\behaviors\CategorizableBehavior',
	'attribute' => 'grade',
	'type' => 'grade',
],

2. Add a relation to ActiveRecord. eg: getGrade for grade

public function getGrade() {
	return $this->getCategoriesRelation('grade');
}

3. Add attribute (eg: "grade") as safe in rules()