The term "primary physical custody," though frequently employed, is not found in the code. It seems to be the equivalent of "primary caretaker," as used in section 3086. The significance of the latter term is explained in Hogoboom and King, California Practice Guide: Family Law 1 (The Rutter Group 1995) paragraph 7:361, page 7-89: "Joint custody orders can complicate the administration of public assistance programs. To alleviate the problem, the court is authorized to specify one of the parents as the `primary caretaker'...."
I haven't read the Practice Guide, but the quote seems to reinforce the code previously mentioned - any such designation is strictly related to public assistance/aid.
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