The Four Rules of Evolvability
Can be accomplished by expressing these four parameters as part of the protocol:
- What it is (identify extension)
- A URI identifies the extension in the global URI space
- May be resolvable (interface description, code, etc.)
- How to deal with it (optional or mandatory)
- Can recipient ignore it or not?
- Who should deal with it (hop-by-hop or end-2-end)
- Should this go to the proxy or the user-agent, origin server
- When to deal with it (ordering)
- First do this; then do this etc.