anchor.diff:  non-nil.")
   
        (must-match-p :always
  -                   :type must-match-choices
  +                   :type (or must-match-choices null)
                      :documentation
                      "Control what to do when input does not match anything.
   - `:always': Reject input.
  
positive.code: ;; We must eval the class at read-time because `make-source' is generated using
  ;; the initargs of the class.
  (sera:eval-always
    (define-class prompter-source ()
      ((name ""
             :documentation
             "Name which can be used to differentiate sources from one
  
negative.code:      (filter #'fuzzy-match
               :type function
               :documentation
               "Takes `input' and a `suggestion' and return a new suggestion, or
  nil if the suggestion is discarded.")
  
       (filter-preprocessor #'delete-inexact-matches
                            :type (or null function)
  