The definition of the 'synonym' property says:

> This property contains an alternative code that may be used to identify this concept instead of the primary code

that's unclear. Is it meant to be defining a code that is an alternative code, or referencing a separately defined code?

I believe that we've decided it should be the second, and we should state that clearly. However it's possible that we can't make it a hard rule for procedural reasons (normative!), so we could only make that a SHOULD not a SHALL