Write a few bars and the machine learns where your melody tends to go — which note follows which — then keeps going there. That's a Markov chain, the oldest trick in algorithmic composition. Order sets how much context it remembers (two notes hold your phrases together better than one); temperature sets how adventurous it is — near 0 it loops your most-travelled paths, past 1 it starts taking the roads you rarely took. Every note it emits came from your seed, so it can't leave the key.
draw a seed, then press “continue”