According to the
specs, we have this:
Quote:
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The date element has one optional OPF event attribute. The set of values for event are not defined by this specification; possible values may include: creation, publication, and modification.
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Readium uses it like this:
Quote:
EPUB 2.x
The string is the value of the <dc:date> element whose opf:event attribute has the value publication.
EPUB 3.x
The string is the value of the <dc:date> element.
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Calibre, on the other hand, seems to ignore altogether the
opf:event property. It just uses the
oldest date, regardless of its attribute.