I am planning to publish a book and I am wondering whether to distribute it as ePub3 or ePub4. My concern being that older eBook readers may still be out there and I do not wish to exclude them. I would prefer ePub3 if the older readers are able to read it.
6
closed as unclear what you're asking by Ian, Anthon, aman207, Danubian Sailor, Flyk Dec 23 '13 at 18:48
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It is unclear what you mean: are you asking if older readers support ePub4 or if new ones support ePub3? – Ian Dec 19 '13 at 22:49
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I believe you are confusing ePub2.0 vs ePub 3.0. If I recall ePub 4 is for Google only. If you are worried about older devices I would focus on validating your .epub file with a 2.0 validation tool.
To answer your question if its backwards, yes, only if it validates across the board:
Example:
<File>
<Name>foo.epub</Name>
<ValidationReport elapsedTimeInMillis="230">
<Version>3.0.0</Version>
<Valid>yes</Valid>
<Errors size="0"/>
<Warnings size="0"/>
</ValidationReport>
<ValidationReport elapsedTimeInMillis="177">
<Version>1.2.0</Version>
<Valid>yes</Valid>
<Errors size="0"/>
<Warnings size="0"/>
</ValidationReport>
<ValidationReport elapsedTimeInMillis="149">
<Version>1.1.0</Version>
<Valid>yes</Valid>
<Errors size="0"/>
<Warnings size="0"/>
</ValidationReport>
<ValidationReport elapsedTimeInMillis="156">
<Version>1.0.5</Version>
<Valid>yes</Valid>
<Errors size="0"/>
<Warnings size="0"/>
</ValidationReport>
<ValidationReport elapsedTimeInMillis="201">
<Version>1.0.4</Version>
<Valid>yes</Valid>
<Errors size="0"/>
<Warnings size="0"/>
</ValidationReport>
<ValidationReport elapsedTimeInMillis="182">
<Version>1.0.3</Version>
<Valid>yes</Valid>
<Errors size="0"/>
<Warnings size="0"/>
</ValidationReport>
<ValidationReport elapsedTimeInMillis="193">
<Version>1.0.2</Version>
<Valid>yes</Valid>
<Errors size="0"/>
<Warnings size="0"/>
</ValidationReport>
<ValidationReport elapsedTimeInMillis="208">
<Version>1.0.1</Version>
<Valid>yes</Valid>
<Errors size="0"/>
<Warnings size="0"/>
</ValidationReport>
</File>
The reason is because an .epub file can be accepted by some as a 3.0 valid ePub ONLY and it could still fail the ePub 2.0 validation.
