Basic on the FHIR specification website.

Basic is used for handling concepts not yet defined in FHIR, narrative-only resources that don't map to an existing resource, and custom resources not appropriate for inclusion in the FHIR specification.

The body should be a list of valid JSON patches for Basic. For example, to update a Slot status to busy, this would be the body:

[
  {
    op: 'replace',
    path: '/status',
    value: 'busy',
  },
],