[cjpearson]

Yes, I think their phrasing in that sentence is vague. It should be structured like the functionality one to make clear that tipping _may_ be added, but if implemented it _must_ use in-app purchases.

However, since tipping is not listed in the exceptions, one should read it as not being allowed.

[enragedcacti]

Agreed, from historical context it definitely seems like the intention was confirming for developers that tipping is a valid use case for IAP and not creating an exemption, but I can see why a motivated party would read it differently, and it is made even more confusing by the App Store review notice seemingly acknowledging that some tips are exempt.