...and from the T3 advance info:

Song playback is also enhanced by the addition of Song Position markers. The idea is that during the playback of a Midi file, it is possible to mark a point to repeat to later. As an example, if a singer wished to sing an extra chorus of a Midi file you were using, simply make a mark at the start of the last chorus. At the end of the chorus, press the Song Position button, and the file will automatically jump back to the marked position at the start of the chorus. This feature gives total flexibility to the length of Midi files, enabling a live feel from pre-recorded songs.