Interesting introduction to the history of musical annotation and copyright.
The journey to that sheet music copyright began with Greek and Roman grammarians; they had developed signs to guide declamation (high voice, low voice and falling voice).
In the mid-1000s, medieval music scholar and teacher Guido of Arezzo decided there needed to be a better way to teach novices. Consequently, he “revolutionized the music education methods of his time.” His innovations made it possible to read music, for a signer to perform a chant that he had not heard before. —WiredPen