We don't want to use Questionnaire.url because that is the identifier for the questionnaire instance itself.  We will update the profile to indicate that Questionnaire.url is not supported for contained adaptive Questionnaires (and is encouraged to be omitted).  However, rather than using Questionnaire.identifier, we will instead use Questionnaire.derivedFrom to point to the Questionnaire.url of the "official instrument" - e.g. the URL for PROMISE. We will continue to have QuestionnaireResponse.questionnaire point to the contained Questionnaire id (i.e. "# [id] ").  However, to support finding responses to adaptive questionnaire instruments (where the QuestionnaireResponse points to a contained resource), we will change the search parameter definition for QuestionnaireResponse 'questionnaire' to search both on QuestionnaireResponse.questionnaire as well as QuestionnaireResponse.questionnaire.resolve().derivedFrom in situations where QuestionnaireResponse.questionnaire is a reference to a contained resource.