I learned from Anne-Marie's video tutorial on Lynda.com that on a Mac for complex technical reasons, you can't Zip up an EPUB from the Desktop. The best solution is a pair of scripts to Unzip and Zip an EPUB. They're called EPUB Zip and EPUB Unzip. This avoids having to use Mac Terminal (which is what Liz Castro uses). She says, "Read the full thread about these on mobileread.com forum, “ePub Zip for Mac OS X”. I think you'll find them with a Google search for "EPUB Unzip" Alternatively, if you use a great XML editor like Oxygen Author (about $200), it lets you work within the archive without unzipping and rezipping.
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