anchor.diff:                        "Whether multiple candidates can be marked.")
   
      (resumer nil
  -            :type (or null (function (source)))
  +            :type (or null function)
               :documentation
               "Function meant to be called with the source as argument when the
   prompter is resumed.
  
positive.code: - the input.")
  
     (filter-postprocessor nil
                           :type (or null (function (list source string) list) function-symbol)
                           :documentation
                           "Function called when input is modified, after
  filtering the suggestions with `filter'.
  
negative.code: - (optional) current input.")
  
     (filter #'fuzzy-match
             :type (or null function function-symbol)
             :documentation
             "Takes a `suggestion', the `source' and the `input' and return a new
  suggestion, or nil if the suggestion is discarded.")
  
     (filter-preprocessor #'delete-inexact-matches
                          :type (or null function function-symbol)
                          :documentation
                          "Function called when
  input is modified, before filtering the suggestions.
  