The revelation comes in the trailer to an upcoming documentary on Arlen and Harburg, “The Sound of Oz,” being assembled by Harburg’s great-grandson, Aaron Harburg. Among others, the younger Harburg is interviewing celebrities who have been associated with “Oz” in various ways, to show how the film has influenced world culture.

Here is a trailer for the upcoming film. In it, Schwartz says he hid “Oz” passages in five places in Wicked and plays one example, starting at the 1:40 mark.

Schwartz says he wrote seven notes of “Defying Gravity” to match the first seven notes of “Over the Rainbow,” corresponding to the words “Unlimited. Together…”

Harburg says he is trying to crowd-fund the film via Indiegogo at https://www.indiegogo.com/projects/the-sound-of-oz. The film has its own website, www.thesoundofozmovie.com.