FHIR: Using a relative date in Search or Subscription Criteria -

is possible use relative date or calculated value in either search request or subscription criteria? necessary in subscription criteria, criteria value saved in resource.

i able provide functionality this:

subscribe patients patient less 2 years old. search patients on 65 years old. search observations in last week.

thanks in advance.

it's possible define custom search criteria involve sort of calculation or inference on part of responding server, though increases complexity server responding query. once defined, these used subscriptions well. if think there's broad utility particular derived query parameter, can propose inclusion in specification well.