As raised on the mailing list by @johnfoliot, the purpose of the landmarks nav and what links authors are supposed to add to it is not very clear in the specification. There is also little and inconsistent use of landmarks in reading systems.

To try and remediate some of the confusion problems for authors, we may want to look at:

• clarifying that the landmarks must be a flat list of entries (no nested lists)
• providing some guidance about limiting the number of entries for ease of access when presented to users (it's not supposed to be a reproduction of the table of contents)
• providing guidance about the preferred type of entries (e.g., select reference links and front/body/back matter)
• informatively noting that the links may be exposed directly to users, so should have readable labels

Other suggestions welcome.