I did find https://docs.oasis-open.org/office/v1.2/OpenDocument-v1.2-part1.html#ForeignElementsAndAttributes and https://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part1.html#Namespaces which lists (in this case for OpenDocument 1.2) the standards-compliant XML namespaces, but even a cursory look at one document indicates that it includes *many* XML namespaces not in that list even though those aren't even relevant to the type of document (for example, an OpenDocument text document including a "calcext" Document Foundation Calc schema, which I feel confident saying should *not* be used in any way in that document).
