Observation lastn

As part of identifying the latest HPO terms applicable to a patient, servers MAY implement the $lastn operation, which uses the Observation search parameters to filter results and restricts the return of matching resources to the last n Observations for the patient. e.g. for the latest Renal Insufficiency HPO code value for Meir Lieberman:

GET [base]/Observation/$lastn?max=1&patient=Patient/Patient-MeirLieberman-Example&code=https://hpo.jax.org/app/|HP:0000083