HTTP is the application layer protocol that MUST be used for requests and responses. Accordingly, unless overridden explicitly hereunder, the rules governing the semantics of HTTP requests and responses apply from RFCs 7230-7237.
In particular, GRNconnect server ensures that the method GET is safe (i.e. its semantics are read-only) in the sense of RFC 7231. In addition to that safe method, DELETE and PUT are idempotent (i.e. multiple invocations have the same effect as that of the first such).