subject_token_type for Replacement Txn-Token Request

[dteleguin]

In 7.5.2:

To request a replacement Txn-Token, the requester makes a Txn-Token Request as described in Section 7.1 but includes the Txn-Token to be replaced as the value of the subject_token parameter.

Does this assume that subject_token_type should be urn:ietf:params:oauth:token-type:txn_token? Should we call it out explicitly?

[gffletch]

Yes, I think that makes sense.