EPUB 3 Best Practices

Chapter 11. Validation

To paraphrase a common expression, there are three things you need to know about a finished EPUB 3 file: it must adhere to rules, rules, and damned rules.

Which is only to say that there is nothing unique about EPUB 3 as a document publishing format. The rules are there to ensure that your content can be opened and rendered by any reading system. They can’t tell you how your content will look on any given reading system, but they can alert you to bugs that are the result of bad markup. If you skip the validation stage and assume that just because it seemed to be fine testing in a reading system, or a program exported it so it must be valid, you run the risk of a lot of wasted time and effort later.

Some vendors will prevent your file from being distributed if it doesn’t validate (which is a good thing), in which case you’ll be forced back to this step right away should you try to avoid it. Others may not, or you might distribute the file yourself, in which case it might only be as you get flooded with angry emails from customers that you’ll learn all the things you did wrong. Once your reputation is tarnished, even if just in a comments section on a product page, it can be hard to get back. No one appreciates someone who hasn’t bothered to do basic validation to ensure their content renders, after all.

This chapter is last in the book not only because it wouldn’t make sense to talk about validation before understanding EPUB content, but also because it diverges ...