CIP57: purpose in datum objects

[nielstron]

Some [frameworks] may chose, for example, to abstract [...] away from their users. Which is why we only make the purpose an optional field (except for datum) to leave a bit of flexibility for blueprint producers. For consumers, we recommend to treat purposes as discriminants to refine interfaces, but assume that a validator without purpose simply apply to any purpose. (https://cips.cardano.org/cips/cip57/#purpose)

I am understanding this (and also reading the Example such that) the datum field of the blueprint must always contain a purpose field. Moreover, the purpose of a datum must be spend, because no other invocation purpose of a smart contract allows for the presence of datums. Is this intended? Should it be made explicit?