1. The agreement referred to in Article 5(1) and (2), shall be expressed in writing, dated and signed by both spouses. Any communication by electronic means which provides a durable record of the agreement shall be deemed equivalent to writing.2. However, if the law of the participating Member State in which the two spouses have their habitual residence at the time the agreement is concluded lays down additional formal requirements for this type of agreement, those requirements shall apply.3. If the spouses are habitually resident in different participating Member States at the time the agreement is concluded and the laws of those States provide for different formal requirements, the agreement shall be formally valid if it satisfies the requirements of either of those laws.4. If only one of the spouses is habitually resident in a participating Member State at the time the agreement is concluded and that State lays down additional formal requirements for this type of agreement, those requirements shall apply.