4. Redefined uid Property

The type signature of the uid property from Section 2.1.9 of [RFC9553] is redefined.

OLD:

|  *uid: String (mandatory).*

NEW:

|  *uid: String (optional).*

The remaining property definition is unchanged, with this additional rule: a Card without a uid property cannot be referred to as a group member in the members property or placed in relation to another Card object through the relatedTo property.