MathML fall-back image

mrprobert · 02-14-2025, 08:39 PM

Hi,

With an epub containing MathML equations, "Delete Unused Media Files" wants to delete the fall-back image specified in the altimg attribute. Is there an error in the attached exemplar? Is there something I need to add? Thank you for your advice.

Sigil 2.4.2, Windows 10.

KevinH · 02-15-2025, 08:36 AM

What altimg attribute? Is this part of MathML3 spec?

You might want to see this link:

https://github.com/w3c/epub-specs/issues/1268

The only mention I could find was in the epub 3.1 spec back in 2017

https://www.w3.org/submissions/2017/...docs-20170125/

But since those fallbacks were never supported by any e-readers, support was dropped in later epub3.2 and now 3.3 specs.

So technically these are unused images under the latest spec.

KevinH · 02-15-2025, 10:48 AM

All that said, I could add math tag altimg attributes as potential for holding image resources so that they are considered to be used.

KevinH · 02-15-2025, 11:45 AM

I thought about this a bit more and since it was a part of the 3.1 epub spec and so could exist in the wild and because altimg is part of the MathML 2.0 (not yet part of w3c html or epub spec), it would not hurt to detect its use and to update it if the underlying image resource is ever renamed or moved (or if the file using of this attribute moves locations). And of course to detect that image was used by Sigil.

So I have hopefully pushed a change to Sigil master to support that. But since Preview is browser based (and all browsers now support mathml - even chrome) and it also has MathJax3, I have no device to test if this altimg attribute is ever used.

This "fix" will appear in the next release of Sigil.

Thank you for your bug report.

mrprobert · 02-15-2025, 03:43 PM

Kevin,

Thank you for your reply. altimg is in the Mathematical Markup Language (MathML) Version 3.0 2nd Edition recommendations, and it is in the Mathematical Markup Language (MathML) Version 4.0 working draft but marked as not core MathML.

Does the epub 3 support only core functions?

https://www.w3.org/TR/MathML3/chapter2.html#fund.syntax
https://www.w3.org/TR/mathml4/

mrprobert · 02-15-2025, 03:45 PM

Oh by the way, epubcheck doesn't flag altimg as errant.

KevinH · 02-15-2025, 03:49 PM

As far as I know yes, just the core. More recent browsers use a living html spec but exactly what aspects are supported is not well publicized. The epub spec people in epub3.2 and epub3.3 have focused only on including things that most shipping epub3 ereaders and some browsers actually support. Thus the link pointing to dropping the rec to use altimg.

02-15-2025, 08:36 AM	#2
KevinH Sigil Developer Posts: 8,759 Karma: 5706256 Join Date: Nov 2009 Device: many	What altimg attribute? Is this part of MathML3 spec? You might want to see this link: https://github.com/w3c/epub-specs/issues/1268 The only mention I could find was in the epub 3.1 spec back in 2017 https://www.w3.org/submissions/2017/...docs-20170125/ But since those fallbacks were never supported by any e-readers, support was dropped in later epub3.2 and now 3.3 specs. So technically these are unused images under the latest spec. Last edited by KevinH; 02-15-2025 at 10:43 AM.

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02-15-2025, 10:48 AM	#3
KevinH Sigil Developer Posts: 8,759 Karma: 5706256 Join Date: Nov 2009 Device: many	All that said, I could add math tag altimg attributes as potential for holding image resources so that they are considered to be used.

02-15-2025, 11:45 AM	#4
KevinH Sigil Developer Posts: 8,759 Karma: 5706256 Join Date: Nov 2009 Device: many	I thought about this a bit more and since it was a part of the 3.1 epub spec and so could exist in the wild and because altimg is part of the MathML 2.0 (not yet part of w3c html or epub spec), it would not hurt to detect its use and to update it if the underlying image resource is ever renamed or moved (or if the file using of this attribute moves locations). And of course to detect that image was used by Sigil. So I have hopefully pushed a change to Sigil master to support that. But since Preview is browser based (and all browsers now support mathml - even chrome) and it also has MathJax3, I have no device to test if this altimg attribute is ever used. This "fix" will appear in the next release of Sigil. Thank you for your bug report.

02-15-2025, 03:43 PM	#5
mrprobert Connoisseur Posts: 71 Karma: 46 Join Date: Mar 2017 Device: None	Kevin, Thank you for your reply. altimg is in the Mathematical Markup Language (MathML) Version 3.0 2nd Edition recommendations, and it is in the Mathematical Markup Language (MathML) Version 4.0 working draft but marked as not core MathML. Does the epub 3 support only core functions? https://www.w3.org/TR/MathML3/chapter2.html#fund.syntax https://www.w3.org/TR/mathml4/

02-15-2025, 03:45 PM	#6
mrprobert Connoisseur Posts: 71 Karma: 46 Join Date: Mar 2017 Device: None	Oh by the way, epubcheck doesn't flag altimg as errant.

02-15-2025, 03:49 PM	#7
KevinH Sigil Developer Posts: 8,759 Karma: 5706256 Join Date: Nov 2009 Device: many	As far as I know yes, just the core. More recent browsers use a living html spec but exactly what aspects are supported is not well publicized. The epub spec people in epub3.2 and epub3.3 have focused only on including things that most shipping epub3 ereaders and some browsers actually support. Thus the link pointing to dropping the rec to use altimg.

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