My client is uploading my epub file to the ibookstore, and has been getting the "ERROR ITMS-9000." I'm cringing as my epub that passed the threepress epub check causes my clients grief.
No luck finding the Metadata, File Formats and Cataloging in the iBookstore FAQs.
I did find an article about which characters are allowed in URIs, including "%encoding"
http://www.rfc-editor.org/rfc/rfc3986.txt. There's an appendix that gives a hierarchy of reserved and unreserved characters.
Susan