Possible Clues:

• Supplementary material at the end of a document
• Extra bit from novel I quietly expand
• It's part of the large intestine? Presumably, I read that it in a book!
• Writer's addition that may be removed when it gets to the theatre
• Subsidiary section
• Download tip backing team: it may be found in a book
• One may have to have it out with a priest to finish before nine
• Key pages next to what might be index
• Section at end of a book
• Phone software design — one shown by Times Supplement