The "Caretaker Doctrine" provided that the "primary caretaker" of the child would maintain custody - so long as both parents were otherwise equally fit to raise the child. The 1982 case of Commonwealth v. Jordan established the "caretaker doctrine" in Pennsylvania. It has not often been used since then, because shared physical custody is (unofficially) becoming more common and both parents are rarely "equally fit".
In the recent case of M.J.M. v. M.L.G, 63 A3d 331 (2013), the Pennsylvania Superior Court declared that the Caretaker Doctrine was dead. The 2011 Pennsylvania custody amendments created 16 factors for the court to consider when awarding custody. The Superior Court found that these factors overrode the prior Doctrine, especially because one of the factors resembled the Caretaker Doctrine and thus replaced that doctrine. In short, the identity of the primary caretaker is but one of many factors in making an award of custody.
Because the Court also found that both parents were not "equally fit", the elimination of the Caretaker Doctrine was not a necessary step in the decision. So, the court's statement that the 2011 custody law overrode the Caretaker Doctrine is non-binding "dicta". However, the Doctrine was little used anyway and it is clear that the Court believes that the Doctrine is dead. This is but one more movement towards enshrinement of the 15 controlling factors fro custody.