I find the spec slightly confusing around data URLs:

• the "Data URLs" section says resources in data URLs are not publication resources.
• the publication resource definition says data URLs are an exception to the requirement to list publication resources in the manifest, which kinda implies resources in data URLs are publication resources.

Which is true?
Can a data URL be listed in the manifest? (the manifest MUST only list publication resources)
If yes, a navigation document that is not in the spine can be defined as a data URL… do we need more restrictions?