FHIR is designed for lightweight exchange of information and CDA is an existing and successful standard for supporting transacting large volumes of data for transitions of care. It's not clear what problems this guide is attempting to solve with FHIR that aren't already solved by CDA (or perhaps a minor update to existing CDA). We are concerned that energy may be spent reinventing solutions to already solved problems; if a developer sees multiple standards to solve a given problem, it will force some developers to build both implementations rather than focusing on one to be compatible across the industry. Please clarify in the guide what problems this solves that CDA cannot so that developers will understand where this guide applies and when to use CDA.