epub3 to epub2 compatibility

PilcrowandStanza · 11-09-2024, 12:50 AM

Hi all,

Book designer here. Still struggling with the ebook end of things.
I'm having trouble getting my epub3 files to work on epub2-only readers/apps

I'm exporting from InDesign, then cleaning things up in Sigil
(I'm a print-first designer). My understanding was that epub3 files automatically downgrade to epub2 where 3 isn't supported, but that doesn't seem to be the case.

For example, on my Mac, the epub3 automatically opens in Books, which does not seem to support that format because the page breaks are missing, but if I export it as epub2, it looks fine.

So, is there something missing to ensure that files downgrade to epub2? An if/then kind of thing? (I'm a coding n00b, sorry)

Note that I mostly want the accessibility features (screen-reading, etc) to be available to those who need it. Also, the pop-up footnote thing is handy.

All tips, tricks, advice, clear instructions welcome.

Thanks!

Turtle91 · 11-09-2024, 08:23 AM

Short answer: no. ePub 3 does not automatically devolve into ePub 2.

Good news is that you can create your css to take advantage of the ePub standard which requires that unknown css must be ignored gracefully. So, you put your ePub2 styling first, then include your ePub3 styling after (closer to the bottom) on your stylesheet. If it doesn’t understand (or support) your ePub3 styling then it reverts to the most recent settings it DOES understand (the ePub2 styling). This is referred to as ‘fallback coding’.

Unfortunately some of the older, but still common, devices have a bug in which they completely throw out the entire css stylesheet if there is something it doesn’t like on it - VERY frustrating! @Rbnjrg posted a technique he uses to work around this bug - you can search for the very recent thread (sorry I’m on my phone or I would link it).

Rbnjrg’s method is to use a simple JavaScript which is only supported by ePub 3 devices. If it supports ePub3/js then the script links a second, ePub3, stylesheet. Older, ePub2 only, devices won’t run the script and will never ‘see’ the ePub3 styling.

Have fun with the new book format!

KevinH · 11-09-2024, 08:52 AM

In Sigil, to make an epub3 more compatible with epub2, you should use the epub3 tools menu to create the epub2 NCX toc.ncx and update the opf guide from the current epub3 nav.

And using correct fallback css is also important.

Just understand there are a bunch of old broken epub2 and even some broken epub3 e-readers out there.

11-09-2024, 12:50 AM	#1
PilcrowandStanza Member Posts: 12 Karma: 10 Join Date: Dec 2023 Device: none	epub3 to epub2 compatibility Hi all, Book designer here. Still struggling with the ebook end of things. I'm having trouble getting my epub3 files to work on epub2-only readers/apps I'm exporting from InDesign, then cleaning things up in Sigil (I'm a print-first designer). My understanding was that epub3 files automatically downgrade to epub2 where 3 isn't supported, but that doesn't seem to be the case. For example, on my Mac, the epub3 automatically opens in Books, which does not seem to support that format because the page breaks are missing, but if I export it as epub2, it looks fine. So, is there something missing to ensure that files downgrade to epub2? An if/then kind of thing? (I'm a coding n00b, sorry) Note that I mostly want the accessibility features (screen-reading, etc) to be available to those who need it. Also, the pop-up footnote thing is handy. All tips, tricks, advice, clear instructions welcome. Thanks!

11-09-2024, 08:52 AM	#3
KevinH Sigil Developer Posts: 8,403 Karma: 5702578 Join Date: Nov 2009 Device: many	In Sigil, to make an epub3 more compatible with epub2, you should use the epub3 tools menu to create the epub2 NCX toc.ncx and update the opf guide from the current epub3 nav. And using correct fallback css is also important. Just understand there are a bunch of old broken epub2 and even some broken epub3 e-readers out there. Last edited by KevinH; 11-09-2024 at 07:37 PM.

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11-09-2024, 08:23 AM	#2
Turtle91 A Hairy Wizard Posts: 3,285 Karma: 20171067 Join Date: Dec 2012 Location: Charleston, SC today Device: iPhone 15/11/X/6/iPad 1,2,Air & Air Pro/Surface Pro/Kindle PW & Fire	Short answer: no. ePub 3 does not automatically devolve into ePub 2. Good news is that you can create your css to take advantage of the ePub standard which requires that unknown css must be ignored gracefully. So, you put your ePub2 styling first, then include your ePub3 styling after (closer to the bottom) on your stylesheet. If it doesn’t understand (or support) your ePub3 styling then it reverts to the most recent settings it DOES understand (the ePub2 styling). This is referred to as ‘fallback coding’. Unfortunately some of the older, but still common, devices have a bug in which they completely throw out the entire css stylesheet if there is something it doesn’t like on it - VERY frustrating! @Rbnjrg posted a technique he uses to work around this bug - you can search for the very recent thread (sorry I’m on my phone or I would link it). Rbnjrg’s method is to use a simple JavaScript which is only supported by ePub 3 devices. If it supports ePub3/js then the script links a second, ePub3, stylesheet. Older, ePub2 only, devices won’t run the script and will never ‘see’ the ePub3 styling. Have fun with the new book format!

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