Section

https://www.w3.org/TR/epub-34/#sec-epub-type-attribute

Describe the problem

When we specify default vocabularies, we typically provide their prefix URL, but epub:type in content documents just says that the structural semantics vocabulary is the default vocabulary. The section doesn't include a prefix URL for expanding the terms.

Describe the fix or new feature you propose

If I go back to 3.0.1, although there still isn't an explicit statement of the URL, it's clear from the references section that we intended the prefix URL to be:

http://www.idpf.org/epub/vocab/structure/#

That matches the pattern used for the other default vocabs we established.

We should make this clearer, though, for anyone looking to create full URIs from the values.

(The omission was brought to my attention by the Readium folks, so it's not just a hypothetical need.)