type Subdivision = "1m" | "1n" | "2n" | "2t" | "4n" | "4t" | "8n" | "8t" | "16n" | "16t" | "32n" | "32t" | "64n" | "64t" | "128n" | "128t" | "256n" | "256t" | "0"

Represents a subdivision of a measure. The number represents the subdivision. "t" represents a triplet. e.g. "4n" is a quarter note, and "4t" is a quarter note triplet.