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KevinH · 03-29-2023, 08:09 AM

Unfortunately, that was 2009 and even by 2015 fallbacks were still not accepted by most epub reading systems.

See this epubcheck issue post from 2015 for example:

https://github.com/w3c/epubcheck/issues/511

And as pointed out, fallbacks are a feature of the e-reader and not Sigil. It is up to the e-reading system to decide if and how to handle fallbacks. As a design tool, Sigil should allow the user to create fallbacks that must then be tested on multiple e-readers.

Sigil supports all epub3 core media types. But application/pdf is not a epub3 core media type and so is not guaranteed to be supported by epub e-readers.

I could add support for recognizing the application/pdf mime type in Sigil, but given the horrendous state of e-reader fallback support and all of the issues Jelby mentioned, it would be a real mistake for anyone to use it for a commercial epub.

Not even all browser engines support pdf without additional plugins.

I will at least change Sigil to not replace it but frankly embedding a pdf inside an epub is not a good idea (IMHO). Contrary to public opinion an epub is not a website just rolled into a zip and never should be.

Update:
Even worse, to be epubcheck legal you must create an xhtml or svg version of the pdf and label it as the fallback. Once you have an xhtml or svg version of the pdf, why on earth include the pdf at all? I think Adobe ADE2 / ADE4 supporting pdf is just Adobe pushing its own products and trying to extend the spec just like they tried with their multi-column layout, font obfuscation rules, and pagemap.xml.

Update 2:
FWIW, neither Thorium or Readium e-readers work with that Gulliver's Travels test epub at all.

03-29-2023, 08:09 AM	#3
KevinH Sigil Developer Posts: 8,841 Karma: 6120478 Join Date: Nov 2009 Device: many	Unfortunately, that was 2009 and even by 2015 fallbacks were still not accepted by most epub reading systems. See this epubcheck issue post from 2015 for example: https://github.com/w3c/epubcheck/issues/511 And as pointed out, fallbacks are a feature of the e-reader and not Sigil. It is up to the e-reading system to decide if and how to handle fallbacks. As a design tool, Sigil should allow the user to create fallbacks that must then be tested on multiple e-readers. Sigil supports all epub3 core media types. But application/pdf is not a epub3 core media type and so is not guaranteed to be supported by epub e-readers. I could add support for recognizing the application/pdf mime type in Sigil, but given the horrendous state of e-reader fallback support and all of the issues Jelby mentioned, it would be a real mistake for anyone to use it for a commercial epub. Not even all browser engines support pdf without additional plugins. I will at least change Sigil to not replace it but frankly embedding a pdf inside an epub is not a good idea (IMHO). Contrary to public opinion an epub is not a website just rolled into a zip and never should be. Update: Even worse, to be epubcheck legal you must create an xhtml or svg version of the pdf and label it as the fallback. Once you have an xhtml or svg version of the pdf, why on earth include the pdf at all? I think Adobe ADE2 / ADE4 supporting pdf is just Adobe pushing its own products and trying to extend the spec just like they tried with their multi-column layout, font obfuscation rules, and pagemap.xml. Update 2: FWIW, neither Thorium or Readium e-readers work with that Gulliver's Travels test epub at all. Last edited by KevinH; 03-29-2023 at 01:40 PM.