Function set 

pub fn set(args: &[Value]) -> Result<Value, EvalError>

jsonb_set(target, path, new_value [, create_missing]) — replace at PG text-array path. create_missing defaults to true.

• Path step on object: treated as key. If missing & create_missing → insert; else no-op.
• Path step on array: integer index, negative counts from end. Out-of-range with create_missing → append; without → no-op.
• Type mismatch (e.g. step on a scalar) → no-op (PG semantics).