anchor.diff:                                     "default" "packed")
                           :message-type :extends ; this message is an extension
                           :documentation documentation)))
  +         (top-level-form-p (top-level-p *protobuf*))
            ;; Only now can we bind *protobuf* to the new extended message
            (*protobuf* extends)
            (index 0))
  
positive.code:           (collect-type-form
             (make-structure-class-forms type slots non-lazy-fields lazy-fields)))
        (collect-form `(record-protobuf-object ',type ,message :message))
        `(progn
           define-group
           ,message
  
negative.code:              (appendf (proto-fields extends) (list field))
               (appendf (proto-extended-fields extends) (list field))))))
        (collect-form `(record-protobuf-object ',type ,extends :message))
        (create-progn-with-enum-forms-if-top-level top-level-form-p forms))))
  
  (defun index-within-extensions-p (index message)
    (let ((extensions (proto-extensions message)))
  