Implementation of EPUB CFI FragmentSelector

[llemeurfr]

In https://github.com/readium/annotations?tab=readme-ov-file#122-selector it is stated that EPUB CFI FragmentSelector for EPUB files. But EPUB CFI implementations are sparse in the world of Reading Systems. What do we do then?

[HadrienGardeur]

I would strongly vote against using CFI as a requirement in this spec.

We've avoided CFI in Readium for several years now and we know that CFI support is inconsistent, not terribly well documented and unavailable in a number of languages that we rely on.

Sticking to other selectors or to widely adopted media fragments on the Web feels like the better option IMO.

A CFI attempts to mash together several pieces of information that are better expressed separately in our case:

• a path to a resource in the publication
• a path into the document tree of a resource
• character/temporal/spatial offsets

[mickael-menu]

Given we don't support reading CFIs in the Readium toolkits, I don't think we should require CFIs for the Annotations document.

[llemeurfr]

I don't disagree, but we need a selector that is a MUST for every implementation of the Annotation model. If not, interoperability will be totally broken.

[mickael-menu]

If it's required and we can't use text selectors, I'd rather have DOM ranges as the requirement for HTML-based publications.

[HadrienGardeur]

I think CSS selectors should be on the table as well for HTML-based publications.

[mickael-menu]

Yes but they are often not enough for a text selection.

[llemeurfr]

Just a note: if the W3C Publishing WG extends EPUB to support vanilla html5 (EPUB 3.4), because EPUB CFIs are tied to XML, they will become unusable on html5 content documents, unless the EPUB CFI spec is re-written accordingly.

[llemeurfr]

Another note: one cannot use EPUB CFI selectors on resources that are declared out of the spine.
see w3c/epub-specs#226, https://groups.google.com/g/epub-working-group/c/15CR6mSf7a0.
These discussions are from 2013: 11 years...

I'm not sure that it is a stroke against the use of EPUB CFIs as lingua franca for annotation selectors.

[HadrienGardeur]

Another note: one cannot use EPUB CFI selectors on resources that are declared out of the spine.

It's an accumulation of issues with CFI that make them completely unfit for this purpose. Not being able to represent a progression/bookmark out of spine is acceptable, but disallowing highlights/annotations on out of spine items is more of an issue.

You've also heard Brady yesterday during the TPAC meeting: CFIs are a pain to deal with, that's reason enough to avoid them (like we've been doing successfully for years in Readium).