- Document expected behaviour.

Author: general-kroll-4-life

docs/developer_guide.md

@@ -268,3 +268,13 @@ time ./stackql exec --cpuprofile=./select-disks-improved-05.profile --auth='{ "g
 ## AWS HTTP request signing
 
 https://docs.aws.amazon.com/sdk-for-go/api/aws/signer/v4/
+
+## Selection from non-select DML
+
+`INSERT RETURNING` can function in two mechanisms:
+
+- Synchronous responses, such as [`google.storage.buckets`](https://cloud.google.com/storage/docs/json_api/v1/buckets/insert).  The returning clause is a projection on the immediately available reponse body.
+- Asynchronous responses, such as [`google.compute.instances`](https://cloud.google.com/compute/docs/reference/rest/v1/instances/insert).  The returning clause is a projection on the reponse body **after** the await flow has concluded.
+
+Future use cases for `UPDATE RETURNING`, `REPLACE RETURNING` and `DELETE RETURNING` will function the same observable fashion.
+