We say:

The default value auto MUST be assumed by Reading Systems as the global value if no meta element carrying this property occurs in the metadata section. Reading Systems MAY support only this default value.

I'm trying to figure out if it's possible to violate this rule. The definition of auto is:

The Author does not have a preference for overflow handling. The Reading System MAY render overflow content using its default method or a user preference, whichever is applicable.

So... say a book has no rendition: flow element. The reading system is therefore obligated to... use the auto value, which means it can choose any of the possible values? It could choose to paginate. It could choose to do scrolled-continuous. It could choose to do scrolled-doc.

Is the original MUST statement thus untestable?