In EPUB 3.3, XHTML requirements says the epub:type attribute MUST only be used on palpable content.

This list is restrictive and will likely cause a lot of existing material being rejected. Several HTML elements like body or li are not palpable content but are often associated an epub:type attribute (they're defined as relevant usage context in the structural semantics vocabulary).

Also, it means epub:type and hidden cannot co-exist, I'm not sure how that's relevant.

Was the idea was to not allow epub:type on some elements like head and style?

If yes, we could either:

• restrict epub:type to any element except metadata content and the html element.
• restrict epub:type to flow content and the body element.