epubcheck validation error: "A fallback must be specified."

Scrivener Scrivener for macOS
1

Hello,

I’ve just finished an epub compile for Kobo, with ‘Adobe Digital Editions page template’ enabled, thus, I had the following errors on checking: “A fallback must be specified.”

What does it mean, please?
What I have to fix on the epub?

ERROR: /Users/abobeda/SkyDrive/Dezbloqueio/ebooks/Memo?ria Apenas de Leitura/versions/Kobo/Memoria_kobo.epub/OEBPS/Text/contents.xhtml(13,109): non-standard stylesheet resource ‘OEBPS/Misc/page-template.xpgt’ of type ‘application/vnd.adobe-page-template+xml’. A fallback must be specified.
ERROR: /Users/abobeda/SkyDrive/Dezbloqueio/ebooks/Memo?ria Apenas de Leitura/versions/Kobo/Memoria_kobo.epub/OEBPS/Text/body.xhtml(13,109): non-standard stylesheet resource ‘OEBPS/Misc/page-template.xpgt’ of type ‘application/vnd.adobe-page-template+xml’. A fallback must be specified.
ERROR: /Users/abobeda/SkyDrive/Dezbloqueio/ebooks/Memo?ria Apenas de Leitura/versions/Kobo/Memoria_kobo.epub/OEBPS/Text/body1.xhtml(13,109): non-standard stylesheet resource ‘OEBPS/Misc/page-template.xpgt’ of type ‘application/vnd.adobe-page-template+xml’. A fallback must be specified.
ERROR: /Users/abobeda/SkyDrive/Dezbloqueio/ebooks/Memo?ria Apenas de Leitura/versions/Kobo/Memoria_kobo.epub/OEBPS/Text/body2.xhtml(13,109): non-standard stylesheet resource ‘OEBPS/Misc/page-template.xpgt’ of type ‘application/vnd.adobe-page-template+xml’. A fallback must be specified.
ERROR: /Users/abobeda/SkyDrive/Dezbloqueio/ebooks/Memo?ria Apenas de Leitura/versions/Kobo/Memoria_kobo.epub/OEBPS/Text/body3.xhtml(13,109): non-standard stylesheet resource ‘OEBPS/Misc/page-template.xpgt’ of type ‘application/vnd.adobe-page-template+xml’. A fallback must be specified.
ERROR: /Users/abobeda/SkyDrive/Dezbloqueio/ebooks/Memo?ria Apenas de Leitura/versions/Kobo/Memoria_kobo.epub/OEBPS/Text/body4.xhtml(13,109): non-standard stylesheet resource ‘OEBPS/Misc/page-template.xpgt’ of type ‘application/vnd.adobe-page-template+xml’. A fallback must be specified.
ERROR: /Users/abobeda/SkyDrive/Dezbloqueio/ebooks/Memo?ria Apenas de Leitura/versions/Kobo/Memoria_kobo.epub/OEBPS/Text/body5.xhtml(13,109): non-standard stylesheet resource ‘OEBPS/Misc/page-template.xpgt’ of type ‘application/vnd.adobe-page-template+xml’. A fallback must be specified.
ERROR: /Users/abobeda/SkyDrive/Dezbloqueio/ebooks/Memo?ria Apenas de Leitura/versions/Kobo/Memoria_kobo.epub/OEBPS/Text/body6.xhtml(13,109): non-standard stylesheet resource ‘OEBPS/Misc/page-template.xpgt’ of type ‘application/vnd.adobe-page-template+xml’. A fallback must be specified.
ERROR: /Users/abobeda/SkyDrive/Dezbloqueio/ebooks/Memo?ria Apenas de Leitura/versions/Kobo/Memoria_kobo.epub/OEBPS/Text/body7.xhtml(13,109): non-standard stylesheet resource ‘OEBPS/Misc/page-template.xpgt’ of type ‘application/vnd.adobe-page-template+xml’. A fallback must be specified.

Can someone help me, please?

Thank you.

2

Since the Adobe page template isn’t a part of the ePub specification, it wouldn’t surprise me if some validators make a stink about it. That’s why the option was added in the first place, since Apple’s upload validator refuses to submit books with an Adobe page template.

3

For sure.

But, my doubt is:

Does it affect an epub file submission to Kobo, like in the Apple case? Or there is no problem if I send that file to them?

4

I would be surprised if their validator fusses about it (and if it does, they should probably be alerted to the problem), because formatting will be pretty messy on the Kobo without it. I did some tests with stock “perfect validating” ePub files and they look awful on the Kobo. Add the page template in, and suddenly it looks great.