US Copyright Office, Compendium of US Copyright Office Practices… (1984)
“ Standard musical notation, using the five-line, four-space staff is the form most frequently employed to embody musical works. Precision equal to that offered by conventional notation is not required, although the deposit should constitute as precise a representation of the work as possible. Any graphic representation of pitch, rhythm, or both, suffices as long as the notation is capable of being performed. Examples: graphically drawn hand signals, fret notation, staves with more or fewer lines than the conventional staff, and "new music," combining graphic art with music notation. ”
