Fallbacks, fallbacks, fallbacks

So how many fallback methods is too many fallback methods? Or is there such a thing?

EPUB 3 certainly has its share. There are fallbacks for items in the spine, content switching fallbacks at the markup level, element intrinsic fallbacks, manifest fallbacks for content elements, and even binding of media types to scripted fallbacks (before reaching intrinsic fallbacks!).

Sometimes the number of them is directed at compliance with EPUB 2 content, knowing that there would be a transition phase, but looking at each of the methods none is actually specific to backwards compatibility. And remove any of them and you lose some predictability of rendering.

This post isn’t going to be a how-to guide to fallbacks. You can read the details of each in the specs, and there’s an explanation of them in the best practices book. I’m instead going to look at the role fallbacks play and see what patterns arise.
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