The music contains a well-known example of a Picardy third. The author is unknown; the oldest known text was written down by Robert Croo in 1534, and the oldest known setting of the melody dates from 1591.Studwell, W. E. (1995). The Christmas Carol Reader. Haworth Press. pp. 15 There are alternative, modern settings of the carol by Kenneth Leighton and another by Philip Stopford.
