Ways to publish and consume parallels contents

[gautierchomel]

Different discussions and issues are about having similar contents in different forms displayed together or available thru switching mechanism. That applies at least to:

• Same content in two languages which are to be displayed side by side
• Same content in two media type, like images and audio or images and text
• Same content in two displays like fixed-layout and reflow

We previously tried to adress that as synchronised, alternate or fallback but none worked enough to wrap all those cases up. I think we should group all those cases under a parallels contents concept allowing to author contents that could be displayed side by side or switched between.

I suggest to create a dedicated task force to, at least try to, solve that during this charter.

[gautierchomel]

Related issues: #2670 #2825 #2773 #2806

[gautierchomel]

Additional use case: Parallel reading and comparizon of books/papers #2788

parallel reading option for scientific and linguistic comparisons. We need to be able to open say 2 separate books with similar contents and to be able to scroll in both synchronously for comparison and investigation into subjects.

[gautierchomel]

This last one is different as it is about parallelisation across documents. So we have:

• In‑document parallels: multiple representations of the same logical content within one publication (e.g., two languages side by side; text+image; image+audio description; fixed + reflow).​
• Cross‑document parallels: two or more separate EPUBs (or items in the same EPUB) that need synchronised navigation for comparison (e.g., two editions, two translations, article vs. preprint).​

[gautierchomel]

This was discussed 2025-11-27.

Parallel Content

Wendy Reid: we've had use cases for multiple versions of the content and tried to solve with multiple renditions
… parallel content is where there are two or more parts that appear in conjunction with each other
… content in translation is an example where you might have a poem in two different languages on facing pages so you can review each line in each language
… it also comes up in accessibility issues

Gautier Chomel: currently there are different problematics like translated content, fixed and reflow, audio and text

https://www.irccloud.com/pastebin/HohO22uS/

Gautier Chomel: up until now there have been separate discussions and proposals for each but we should try to find one way for all
… I don't have a preferred option for how to address this technically

Ivan Herman: it is an important use case and multiple renditions covers at least some of it
… we don't have a technical solution yet so this group probably can't do it - it likely needs to be incubated in the community group
… I expect the solution will be complicated and needs incubation to figure out what will work

Hadrien Gardeur: multiple renditions does have a mapping document to jump between the renditions - it's a lot like a navigation document
… we need to be careful not to force everything together if they don't work well together
… I think if we modify multiple renditions we could do some interesting use cases like magazines with fixed and reflowable layouts
… we shouldn't reject all of multiple renditions but I agree we do need to look into it more
… the way multiple renditions was defined was not ideal

Wendy Reid: I agree we need incubation - we have bits and pieces of what we need
… if I'm reading a book where one page is one language and another in another language you wouldn't want two separate documents but we don't have multiple reading orders
… same is true for audio where the transcript might be in the same file
… but reflow and fxl probably are always going to require separate documents

Hadrien Gardeur: I think another option for multiple reading orders than multiple renditions and all it entails - a separate publication - we also have collections for alternate reading order
… we wouldn't need to introduce anything new - is worth exploring

Unfortunately, multiple renditions were never really used. Right?

Hadrien Gardeur: I had this in mind at tpac but we didn't have time to discuss - once we're done with comics I'd like to explore it
… we should consider a task force since we're in a revision cycle right now

Ivan Herman: I have practical problems, namely whatever we do if we want to put it in the epub standard we need two implementations
… I get that it's not multiple renditions and it has not been picked up - that's why we took it out and made it a note

If my memory is correct, I think that it is too difficult to use multiple publication documents per zip file.

Ivan Herman: I'm worried about putting something into the standard again before we know that there will be adoption

Wendy Reid: if we are to undertake this a big question is what stopped adoption of multiple renditions - there are some implementations but they are really platform base
… I have a feeling I know why - people didn't know what to do with what we gave them

Hadrien Gardeur: what if we create a task force that does not attempt to introduce new things in the spec
… based on the result of that task force we see whether there is any interest and then decide where to go
… if that fails then we can move it over to the CG to look into further

Gregorio Pellegrino: we shouldn't work in the past but whether it is needed now - EAA is requiring publishers to now produce both fxl and reflow in the same package

Shinya Takami: I wonder if there is enough interest or demand for this - I think it needs more incubation

Ivan Herman: the working group is getting thin and we have existing task forces with a lot of work to do - we should be getting to CR within half a year - so I'm worried about this taking more time away from the revision

Hadrien Gardeur: there is demand for textbooks and it is common for magazines - they are lacking the format to do it
… there is scale now that didn't exist when we did multiple renditions
… the interest is specialized though
… and I agree with Ivan that we shouldn't do too many things at the same time - there is still work for comics but not as much as for annotations
… I can't see doing both in parallel but if we can close comics soon and we get interest in this from other participants then we should at least explore what we can do

+1 to Hadrien Gardeur

Hadrien Gardeur: and if we can't add anything to the spec than it still leaves people with some ideas to work on

Gautier Chomel: scholarly publishing does do multiple renditions but in a closed environment - they need to provide interoperable content
… I understand the time and resource issues but this problem has been around for a long time and should be a priority to finally address
… other solutions are being implemented and it makes it harder to standardize

Wendy Reid: we need to do some outreach to find out who is interested before we get to a task force
… it's easy to start a task force but we don't want to find out later that the work won't be implemented

Gautier Chomel: I think it would be good to have this in the CG because we have more people with interest in this area

+1, anyone can join CG

Hadrien Gardeur: we also have interest in EDRLab but they are not represented in this group

Wendy Reid: for a next step we should start the conversation in the CG
… nothing stops us from promoting the work into the WG later
… doesn't require more work from this group to get it started

Gautier Chomel: I can try by mid-January to have a call in the CG to start a task force