fix(AIP-122): clarify shortening rules for nested collections (#1372)

Author: noahdietz

aip/general/0122.md

@@ -99,11 +99,28 @@ An API **should** use the less-redundant form:
 users/vhugo1802/events/birthday-dinner-226
 ```
 
-In this situation, the _message_ is still called `UserEvent`; only the resource
-name is shortened.
+In this situation, the _message_ and _resource type_ are still called
+`UserEvent`; only the collection and resource identifiers in the pattern(s) are 
+shortened. Since the _resource type_ is not shortened, the `singular` and
+`plural` are similarly _not shortened_.
+
+```
+message UserEvent {
+  option (google.api.resource) = {
+    type: "example.googleapis.com/UserEvent"
+    // Only the collection & resource identfiers in the `pattern` are shortened.    
+    pattern: "projects/{project}/users/{user}/events/{event}"
+    singular: "userEvent"
+    plural: "userEvents"
+  };
+
+  string name = 1;
+}
+```
 
 **Note:** APIs wishing to do this **must** follow this format consistently
-throughout the API, or else not at all.
+throughout all of its `pattern` entries defined and anywhere else the
+resource is referenced in the API, or else not at all.
 
 ### Resource ID segments
 
@@ -357,6 +374,8 @@ isolation of logical concerns per-resource.
 
 ## Changelog
 
+- **2024-06-14**: Clarify resource annotation shortening rules for nested
+  collections.
 - **2023-09-19**: Prohibit duplicate collection identifiers.
 - **2023-09-01**: Add a clause that allows embedding for revision resource
   messages.