O or ‹ or › can be used to define what octave you want to be in. O4 is a deginition while ‹› jusr raise/lower it by one. [] are used for loops. jusr enclose it around some mml and put 0 or blank for infinite, or a # of times to loop. : is a track definition, and you can have 8 playing at once :0-:7. @ is an instrument variable. type mml and then click on the help to find a list of available types