E-readers unable to interpret EPUB 3?

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Newbie question:

I created an EPUB 2 with a list starting at 5 : ol start="5". EpubCheck3 says the attribute "start" is not allowed. So I adjusted my files for EPUB 3 and now EpubCheck validates everything.

If I publish this plain EPUB 3 (no audio / video / animation, etc.), will it be accessible to most ereaders?

In others words, what happens when an e-reader cannot interpret an EPUB 3? Can it still reproduce what it recognizes as part of the EPUB 2 standard?

Hi, effort was made to retain sufficient backwards compatibility in EPUB 3 to enable creation of files that also still work with EPUB 2 reading systems. The main requirement is to put in both the old-style (NCX) and new-style (HTML Navigation Document) table of contents, assuming you want the EPUB 2 system to display a TOC. Also to put in fallbacks if you use new stuff not included in EPUB 2, such as audio/video/animtation (but you said you don't have these). O'Reilly Media has recently moved to distributing EPUB 3 files for all their new titles, see: http://toc.oreilly.com/2013/02/oreillys-journey-to-epub-3.html

However, in the specific case of ol start attribute, which HTML5 "un-deprecated" it may or may not be implemented by older reading systems, which may or may not matter to you (if validation is your primary concern). I would recommend at a minimum testing your content against the latest 2.0 version of Adobe Digital Editions (ADE), which contains the same underlying EPUB 2 "engine" (Adobe RMSDK) as many 3rd party reading devices and apps including Nook, Alkido Reader, Bluefire Reader, OverDrive Media Console, TXTR, etc. If you are OK with how ADE handles your EPUB 3 file you should be OK.

Many thanks, Bill. Your answer is very helpful.

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