In the
Open Container Format (OCF) 3.0 They talk specifically of ZIP: no other format is supported (nor 7z or rar):
Quote:
...
The OCF specification defines the rules for structuring the file collection in the abstract: the "abstract container". It also defines the rules for the representation of this abstract container within a ZIP archive: the "physical container". The rules for ZIP physical containers build upon the ZIP technologies used by ODF....
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I suppose they choose zip because of its diffusion in the world (even in most library and operating system)
OCF is one of the standard ruling ePub format