Music written as words, which ~MX reads when the song compiles and Mx.steps/3 gives its sounds.

Each word lasts one step, and the pattern says nothing of what a word sounds like. _ is silence, - holds the word before it one step longer, and a number after a colon is a word's length in steps, as in g4:2. Words joined by a slash sound together, as in g5/b4, and the words in brackets share one step evenly, as in [f f]. A word after ~ is not struck: the note before it glides to it and lasts through it, as in eb2:2 ~g2:2. A bar line, |, is only for reading. With the modifier s, as in ~MX"9..5 x..."s, each character lasts one step instead: a dot is silence, and spaces and bar lines are left out.

A pattern is a list of cells in order, each a map of its tokens, none for silence, and its length in steps, so two patterns join with ++. A cell that glides has glide: true as well.