Use of HealthCareService as Address book of services for Referrals

The documentation of HealthCareService for STU3 says that it can be used to:

“* Address book of services for Referrals including references to Questionnaires for assessments that are required as part of the referral*”

However there is no obvious element for references to Questionaires (assessments). Can you advise what element should be used or is there another method to do this?