Built-in functions and procedures the engine VM dispatches to. Functions are pure value transformations evaluated mid-query (math, string, json, temporal, casting); procedures are imperative routines that may mutate catalog or storage state and are invoked as named statements. Both are exposed to RQL through stable qualified names that become wire-visible identifiers.
The crate registers every built-in routine with the catalog at boot and resolves user-invoked names against that registry. Renaming a registered routine is a breaking change for queries already on disk, in scripts, and in client code; new routines should be added rather than substituted.