anchor.diff:    (:import-from :shcl/core/posix #:syscall-error)
     (:import-from :shcl/core/posix-types #:dirent #:d-name)
     (:import-from :shcl/core/fd-table #:with-dir-ptr-for-fd #:openat-retained #:fd-release)
  +  (:import-from :shcl-core/exit-info #:exit-info)
     (:export
      #:expansion-for-words #:set-alias #:unalias #:expand #:make-string-fragment
      #:word-boundary #:*split-fields* #:split))
  
positive.code:     (fset:seq (make-string-fragment \"foo\") (make-string-fragment \"bar\" :literal t))
  
  Use word boundaries responsibly.  Check with `*split-fields*' before
  you insert them into your return value."))
  
  (defmethod expand ((thing string))
    (fset:seq (make-string-fragment thing :literal t)))
  
negative.code:          (seqs (if expand-aliases
                     (expand-aliases things)
                     things))
           (exit-infos (fset:empty-seq))
           next-word)
  
      (let ((new-seqs (fset:empty-seq)))
        (fset:do-seq (seq seqs)
          (multiple-value-bind (value exit-info) (expand seq)
            (setf new-seqs (fset:with-last new-seqs value))
            (fset:appendf exit-infos (ensure-exit-info-seq exit-info))))
        (setf seqs new-seqs))
  
      (labels
          ((observe (fragment)
             (unless next-word
  