docs: document naming convention

See toolshed/organising#680

docs/maintainers/handbook.md

@@ -86,6 +86,16 @@ Because configurations are maintained in-repository by maintainers, we version t
 export NGINX_CONFIG_VERSION=v1
 ```
 
+!!! warning
+
+    It is **very important** that the naming convention of the config matches
+    the whole way down. In the above example, that is `nginx_config` in the
+    `configs:` stanza, `nginx_config` in `name:
+    ${STACK_NAME}_nginx_config_${NGINX_CONFIG_VERSION}` and finally
+    `NGINX_CONFIG_VERSION` in the `abra.sh`. This is the naming convention that
+    `abra` will perform to carry out the lookup of all matching names/values.
+    See [`#693`](https://git.coopcloud.tech/toolshed/abra/issues/693) for more.
+
 ## Manage environment variables
 
 !!! warning