My personal gripe is "non-linear". These are pages you shouldn't be able to see just by flipping page-to-page... ideal for "choose your own adventure" type books.
Apple Books doesn't treat these like pages that display only after you tap/click a link though. They render them as a sort of popup above the regular page, styled differently and even with a different page width, as some sort of endnote-not-at-the-end functionality. If that non-linear page also has a link to tap/click on, too bad. Nothing in the spec even slightly suggests their interpretation of it, and the longer they make it the norm, the more impossible it will become to implement the correct functionality because other book titles will have become dependent on it.
Apple Books doesn't treat these like pages that display only after you tap/click a link though. They render them as a sort of popup above the regular page, styled differently and even with a different page width, as some sort of endnote-not-at-the-end functionality. If that non-linear page also has a link to tap/click on, too bad. Nothing in the spec even slightly suggests their interpretation of it, and the longer they make it the norm, the more impossible it will become to implement the correct functionality because other book titles will have become dependent on it.