I seem to remember that Docc was inspired by "The Sough of Horses' Wings" in Ted Lesley's "Paramiracles" (although I think he knew about it before Ted's book was in print.) In that effect, a corner of the page disappears and reappears in a previously empty envelope.
"The Pegasus Page" by Art Emerson appeared in Swami, Vol 2, Issue 13 in the 60's. I find it interesting, but to me, it's not nearly as streamlined as Docc made the effect. In The Pegasus Page, you give the spectator a choice of three books. The book is handed to another spectator to hold while you write the name of the book and the page number on two pieces of cardboard. Give the cardboard to a spectator, the page vanishes from the book, and then appears between the two pieces of cardboard.
Emerson credits the original idea to Herbert Milton, with help from Robert Harbin, and Ned Rutledge.
I think Docc brought the trick down to its most elegant form. You've just got a book and an envelope. And it lends itself to several different presentations.
Also, take a look at one of Bill Goldman's newsletters for his take on it, "Like a Bird on a Wire."