1.6 Images in InDesign
Making Ebooks with InDesign: Module 1, Step 6
Making Ebooks with InDesign: Module 1, Step 5
InDesign to EPUB
Before reading this, you might want to read:
InDesign has a full set of epub:type semantics built in. They are an added layer of semantic inflection that can be applied at the object level to provide an outline to the “bones” of content. Wherever possible, let the HTML do the semantic heavy lifting for you. In a simple chapter, have the body of that chapter wrapped in a <section> tag. But, in order to distinguish that <section> from the <section> wrapping the part title page, for example, you might consider adding in some code that delineates the chapter as such.
A limitation of the core HTML markup grammar is that it is not well-suited for differentiating common publishing structures. There may be hundreds of aside elements in a publication, for example, but reliably identifying which ones represent notes from sidebars from warnings and alerts has not been possible in the past.
For sighted users, the deficiency this causes has been masked by the enhanced visual rendering that CSS style sheets afford (backgrounds, borders and shading are used to convey roles visually). Users of assistive technologies rely on an understanding of the underlying markup in order to facilitate navigation — Web-based technologies have only had limited accessibility because primary and secondary material was often indistinguishable below the visual surface.
To make publications more accessible, you need to consider that many users will be interacting with the content in non-visual ways. To facilitate this, applying semantics allows more precise meanings to be applied to the generic tags.
Buried in the Object —> Object Export Options menu, is a fly-out menu of epub:type options built in there. The full set as defined in the 2011 EPUB 3 spec is there. These kinds of semantics are used to denote the start of frontmatter, bodymatter, and backmatter and can be used to label the many, many elements of book-like content. The behavior of pop-up footnotes, for example, are driven by (in this case) automatically generated epub:type semantics.
The bad news is that epub:type semantics are essentially meaningless. They are not taken up in a meaningful way by any reading systems. (InDesign really needs to update these choices!) I would encourage you to think of epub:type as scaffolding upon which to layer the more meaningful ARIA roles. ARIA roles are a more standard, web-based technology that is better supported in browser and reading systems. There are tools out there that will help you map epub:type to ARIA roles but none I like well enough to recommend. I usually do it by hand. I freely admit that this is an imperfect workflow and more than a little kludgy. But until the InDesign engineers update these semantics, this will have to do when InDesign is a major part of how you get to the EPUB stage.
The epub:type semantics are converted in a landmark navigation in the ebook, which can be seen clearly from Adobe Digital Editions.