feat: updates to several AIPs

aip/general/0160.md

@@ -183,6 +183,15 @@ There are two slight distinctions when parsing messages:
   implementations **may** choose to support automatic conversion between camel
   case and snake case.
 
+For all aforementioned types, simply checking for the presence of a top-level
+resource field is possible with the `*` value:
+
+| Example    | Meaning                                  |
+| ---------- | ---------------------------------------- |
+| `r:*`      | True if `repeated` field `r` is present. |
+| `p:*`      | True if `map` field `p` is present.      |
+| `m:*`      | True if `message` field `m` is present.  |
+
 ### Functions
 
 The filtering language supports a function call syntax in order to support
@@ -231,5 +240,6 @@ Schematic validation refers, but is not limited to, the following:
 
 ## Changelog
 
+- **2025-10-03**: Clarify top-level field has operator behavior.
 - **2025-01-07**: Clarify behavior for unset field in traversal operator chain.
 - **2024-12-11**: Move non-compliant filter guidance to Validation section.