docs: document explicitly quotes in attribute filter

Google APIs · copybara-github · commit b6c0e8abb2e4 · 2022-09-15T16:03:31.000-07:00
PiperOrigin-RevId: 474678911
diff --git a/google/maps/fleetengine/delivery/v1/delivery_api.proto b/google/maps/fleetengine/delivery/v1/delivery_api.proto
@@ -275,7 +275,12 @@ message ListDeliveryVehiclesRequest {
   //
   // Note that the only queries supported for `ListDeliveryVehicles` are
   // on vehicle attributes (for example, `attributes.<key> = <value>` or
-  // `attributes.<key1> = <value1> AND attributes.<key2> = <value2>`).
+  // `attributes.<key1> = <value1> AND attributes.<key2> = <value2>`). Also, all
+  // attributes are stored as strings, so the only supported comparisons against
+  // attributes are string comparisons. In order to compare against number or
+  // boolean values, the values must be explicitly quoted to be treated as
+  // strings (for example, `attributes.<key> = "10"` or
+  // `attributes.<key> = "true"`).
   string filter = 6 [(google.api.field_behavior) = OPTIONAL];
 
   // Optional. A filter that limits the search area to a rectangle defined by the
