anchor.diff:           (or (typep data 'local-time:timestamp)
                (and (stringp data)
                     (chronicity:parse data))))
  -    (validation-error "~A: ~A is not a timestamp"
  +    (validation-error "~A: ~A is not a valid timestamp"
                         (attribute-name attribute)
                         data)))
   
  
positive.code:          (or (typep data 'local-time:timestamp)
               (and (stringp data)
                    (chronicity:parse data))))
      (validation-error "~A: ~A is not a timestamp"
                        (attribute-name attribute)
                        data)))
  
  
negative.code:      (cond
         ((and (not data-attribute)
               (not (attribute-optional-p schema-attribute)))
          (let ((error-msg (or (attribute-option :attribute-required-message schema-attribute)
                               (format nil "Attribute required: ~a"
                                       (attribute-name schema-attribute)))))
            (validation-error error-msg)))
         ((not data-attribute)
  