Explain why #:authentic and #:sealed are there

goblins/core.rkt

@@ -677,6 +677,9 @@
 
 (define (make-become-sealer-triplet)
   (struct become (handler-unseal return-val-unseal)
+    ;; #:authentic and #:sealed, in theory, reduce the scope of
+    ;; how structs might be used in a way that results in a slight
+    ;; speedup (usually, or so it seems)
     #:authentic
     ;; Requires Racket v8.0.0.7+
     ;; but that's been out for a while...