docs: Srds key match doc update. (#9787)

Signed-off-by: Xin Zhuang <stevenzzz@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 0e41d73a4eacfa56bd325aeb40851a2bfe51d28c

envoy/config/filter/network/http_connection_manager/v2/http_connection_manager.proto

@@ -576,7 +576,9 @@ message ScopedRoutes {
       }
     }
 
-    // The final scope key consists of the ordered union of these fragments.
+    // The final(built) scope key consists of the ordered union of these fragments, which are compared in order with the
+    // fragments of a :ref:`ScopedRouteConfiguration<envoy_api_msg_ScopedRouteConfiguration>`.
+    // A missing fragment during comparison will make the key invalid, i.e., the computed key doesn't match any key.
     repeated FragmentBuilder fragments = 1 [(validate.rules).repeated = {min_items: 1}];
   }
 

envoy/extensions/filters/network/http_connection_manager/v3/http_connection_manager.proto

@@ -591,7 +591,9 @@ message ScopedRoutes {
       }
     }
 
-    // The final scope key consists of the ordered union of these fragments.
+    // The final(built) scope key consists of the ordered union of these fragments, which are compared in order with the
+    // fragments of a :ref:`ScopedRouteConfiguration<envoy_api_msg_config.route.v3.ScopedRouteConfiguration>`.
+    // A missing fragment during comparison will make the key invalid, i.e., the computed key doesn't match any key.
     repeated FragmentBuilder fragments = 1 [(validate.rules).repeated = {min_items: 1}];
   }