First, this area of law is placed and put into perspective, vis-à-vis other areas of law and vis-à-vis other systems (economic, sociological, biological, ...).
The law of persons comprises the definition of 'person' (who is a person, from and until when) and identification thereof (names, domicile, sex). After that, the civil status of the person is treated vis-à-vis the State (nationality) and vis-à-vis himself (capacity).
Family law comprises the status of the person in certain relations with other persons. These relations can be vertical or horizontal. Vertical relations are: parentage, authority (deriving from parentage) and kinship (establishment, content and ending). They are usually based on blood ties. Horizontal relations are those between two or more persons who form a socio-economic, and therefore legal, entity. Horizontal relation comprise: marriage, registered and non-registered cohabitation of partners. Establishment, content and ending are dealt with. Nuclear family law is part of family law. Are considered as nuclear families: the horizontal relations and the vertical relations that are part of a socio-economic entity (dependent children or parents).