lib/Query/Common/CriterionVisitor/Field/FieldRelation.php
public function canVisit(Criterion $criterion)
    {
        return
            $criterion instanceof Criterion\FieldRelation &&
            (($criterion->operator ?: Operator::IN) === Operator::IN ||
                $criterion->operator === Operator::CONTAINS);
    }
public function canVisit(Criterion $criterion)
    {
        return
            $criterion instanceof Criterion\FieldRelation &&
            (($criterion->operator ?: Operator::IN) === Operator::IN ||
                $criterion->operator === Operator::CONTAINS);
    }
Check if visitor is applicable to current criterion.

@param Criterion $criterion

@return bool