Rationale   Overall, the "_include" capabilities could provide significant benefits to the FHIR US Core implementation, including improved efficiency, interoperability, data consistency, and user experience. But careful consideration needs to be given to compatibility with other profiles before formally adding support for the "_include" capabilities to US Core. Adding an "_include" capability to US Core is done by including the "_include" parameter in the list of supported parameters for the source resource in the CapabilityStatement. For example, adding an "_include specimen" capability impacts compatibility with other US Core Observation profiles, which do not require the specimen element but share the resource-wide search parameters and Quick Start documentation. Therefore, the reader would need to understand that specific search parameters apply only to certain profiles making it more difficult for developers to understand and implement. This can lead to longer development time and higher costs. For this reason, we have limited this as guidance in the target US Core Specimen Profile.   Proposal   Add guidance and an example query to the Specimen Quick Start Section.       Please note that we have used OpenAI's chatCPG to assist in answering this question. We review these responses and the information provided is based on our experience and implementer feedback and our design choices for US Core.