Now persons routinely trade and travel across state boundaries (both physically and electronically), so the need is to provide stability across state lines given that laws differ from one state to the next. Thus, once defined by the personal law, persons take their capacity with them like a passport whether or however they may travel. In this way, a person will not gain or lose capacity depending on the accident of the local laws, e.g. if A does not have capacity to marry her cousin under her personal law (a rule of consanguinity), she cannot evade that law by travelling to a state that does permit such a marriage (see nullity).