Tom-G
Screenwriter
All of that backstory about the cave and Yoda fighting a dark jedi are all taken from the Expanded Universe, which isn't considered canonical material, but it is fun to read none the less.
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Tom, Are you sure? If I remember the introduction correctly, Zahn claims to have complete consent from Lucas to 'create' what is to become of our heroes after Jedi. My interpretation of that intro was that all the info contained in Zahn's trilogy was to become part of the Star Wars canon. It is those books that were not part of Zahn's trilogy, including other SW books by Zahn himself, that are part of the Expanded Universe.
James, check out this excellent http://www.theforce.net/swtc/continuity.html