Part 3
2 chapters
HTTP semantics done right
Return correct status codes, headers and representations, and do partial updates two correct ways: JSON Patch and Merge Patch.
Chapter 6
Content negotiation & status codes
Serve the right representation for the client's Accept, reject the wrong Content-Type, and return status codes that mean exactly what the spec says — 406, 415, and the 2xx/4xx/409 set.
Chapter 7
Partial updates: JSON Patch vs Merge Patch
Two correct ways to change part of a resource — RFC 6902 JSON Patch and RFC 7396 JSON Merge Patch — their media types, their trade-offs, and when each one is the right tool.