Identifying skippable and escapable roles

[HadrienGardeur]

When using guided navigation, we want to make sure that users are free to automatically skip elements that are irrelevant to them or escape from a number of nested elements.

While escapability could be implemented as a general mechanism for nested elements, identifying specific roles might offer a better user experience.

EPUB 3.3 contains a small list of roles:

• Skippable
  • endnote
  • footnote
  • pagebreak
• Escapable
  • aside
  • figure
  • list
  • table

Aside from a slightly longer list in older versions of the EPUB specification (referencing deprecated roles), I couldn't find a best practice document to cover skippability/escapability.

@danielweck are you aware of such a document? Could you document the list of roles currently supported in Thorium for that?

[HadrienGardeur]

Looking at DPUB ARIA 1.0 and EPUB 3 Structural Semantics Vocabulary, I see a number of roles that act as a container/collections, with an equivalent item element.

All of these roles are IMO good candidates for the list of escapable roles.

Based on the current list of escapable roles, the following ones could be added:

• list-item
• table-row
• table-cell

Looking at DPUB ARIA, I could spot the following roles:

• bibliography
• biblioentry
• credits
• credit
• endnotes
• endnote
• glossary (child roles glossterm and glossdef are not included in DPUB ARIA)
• index (which has many child roles in EPUB 3 Structural Semantics Vocabulary, all missing from DPUB ARIA)

[HadrienGardeur]

Earlier this year, Vital Source shared some information about their approach to skippability: w3c/publishingcg#72 (comment)

They offer two reading modes:

• simplified
• and detailed

The simplified mode automatically skips a number of roles that we've already identified, whereas the detailed one is much more comprehensive.

These roles are also grouped up in what they call filters:

• altText (image for us)
• figure (figure)
• table (table)
• citation (footnotes, endnote and bibliography for us)
• uriLink (we don't have an equivalent yet)
• and math (we're going to add math as well)

I'll need to test their app and see if these filters are configurable beyond the simplified/detailed modes, but overall it seems consistent with what we've documented so far.