extension: .txt

types:
  N: a decimal number represented in ASCII
  S: any ASCII string

consts:
  NL = '\n'
  SEP = ':'

file = header, tracks
header = ntracks, metadata
ntracks = "ntracks", SEP, ntrk:N, NL
metadata = kvpair*
kvpair = key:S, SEP, val:S, NL
tracks = track[ntrk]
track = name:S, NL, event*
event = noteset | metaev
noteset = durspec:N1, cell*, NL
cell = rest | cont | note:N2
rest = ".."
cont = "=="
metaev = kvpair

notes:
  durspec = log2(denominator), e.g., 3 -> eighth
  note = MIDI - 12, e.g., 48 -> middle C