diff --git a/xds/internal/xdsclient/bootstrap/bootstrap.go b/xds/internal/xdsclient/bootstrap/bootstrap.go
index 603f6d94174c..22bdf1dfb287 100644
--- a/xds/internal/xdsclient/bootstrap/bootstrap.go
+++ b/xds/internal/xdsclient/bootstrap/bootstrap.go
@@ -88,9 +88,13 @@ type ServerConfig struct {
 
 // String returns the string representation of the ServerConfig.
 //
-// Note that it covers (almost) all the fields so the string can be used map
-// keys. Except NodeProto because NodeProto isn't used by federation (and this
-// is only used as key in federation).
+// This string representation will be used as map keys in federation
+// (`map[ServerConfig]authority`), so that the stream will be shared by
+// authorities with different name but same server config.
+//
+// It covers (almost) all the fields so the string can represent the config
+// content. It doesn't cover NodeProto because NodeProto isn't used by
+// federation.
 func (sc *ServerConfig) String() string {
 	var ver string
 	switch sc.TransportAPI {