Providing for custody of children by de facto custodians or interested third parties, defining de facto custodian and interested third party; providing for the commencement of proceedings in courts with jurisdiction over child custody matters; requiring the court to grant a hearing on petitions or motions for custody under certain conditions, specifying certain hearing notice requirements; providing for approval of orders without a hearing and for emergency or temporary relief under certain conditions; burden of proof to be on the de facto custodian or interested third party; specifying certain petition or motion content requirements; specifying certain factors to be considered by the court in determining the best interests of the child; providing for de facto and third party custody orders, prohibiting certain court preferences, specifying certain requirements for modification of the orders; requiring persons designated as de facto custodians to be allowed to intervene in custody proceedings; repealing a certain provision providing for relative ex parte temporary custody orders (mk)