Does the proviso "not having a right of custody" mean that only a person who does not have a right to custody may violate section 278 of the Penal Code?

"That manifestly is not the purpose of the proviso that only a person 'not having a right of custody' may violate [Penal Code] section 278 [prescribing punishment for child abduction]. Rather, its purpose is to acknowledge that in the absence of an order or decree affecting the physical custody of the child either parent is privileged (peaceably) to take exclusive possession of the child. [Citations.] Prior to a judicial order depriving a parent of full custody both parents have 'a right of custody.' [Citation.]" (People v. Irwin (1984) 155 Cal.App.3d 891, 896-897, italics added.) An order granting sole custody to one parent, and thus depriving the other parent of custody, such as the judgment in this case, alters the landscape, and makes the presumptions of Family Code section 3010 inapplicable.