In DocumentReference there are two category like fields - Category and Type. Both of these have bindings (example and preferred respectively) to LOINC.

In US Core we created a "Clinical-Note" category as one did not exist in the base specification. I think it would make sense to add a higher-level category option in DocumentReference. A possible place to start would be the concepts (or most of the concepts) described in the resource description:

DocumentReference contains metadata, inline content or direct references to documents such as:

• CDA   documents in FHIR systems
• FHIR documents stored elsewhere (i.e. registry/repository following the XDS model)
• PDF documents  , Scanned Paper, and digital records of faxes
• Clinical Notes in various forms
• Image files (e.g., JPEG, GIF, TIFF)
• Video files (e.g., MP4, WMV)
• Audio files (e.g., WAV, MP3)
• Non-Standard formats (e.g., CSV, RTF, WORD)
• Other kinds of documents, such as records of prescriptions or immunizations