A radio frequency power amplifier and an envelope tracking power supply are disclosed. A plurality of works can be collected together in a list for purposes of establishing a play or a presentation sequence. The clip may include a body member having a first arm and a second arm coupled to the first arm. An absolute radio frequency channel number of a wireless communication system is determined based on the time intervals identified in the first and second lists. The tray can include a slit located at a point along its length that permits the ends of the tray to rotate about the slit so that the ends can be bent with respect to one another.