Pathfinder Roleplaying Game: Planar Adventures - Rules of Play says:
Pathfinder RPG Planar Adventures expands the world of the Pathfinder Roleplaying Game and transports your characters and campaigns into uncanny new worlds rife with both perilous dangers and unimaginable rewards. In these infinite planes of reality, characters will test more than just their mettle against the daunting challenges that confront them—they'll test their very souls!