+ :special t
+ :documentation
+ "Can be T, NIL or :WHEN. In the latter case, attribute is only active if the attribute value is non-null.")
+ (active-attributes :layered-accessor attribute-active-attributes
+ :initarg :attributes
+ :layered t
+ :special t)
+ (active-descriptions :layered-accessor attribute-active-descriptions
+ :initarg :activate
+ :initform nil
+ :layered t
+ :special t)
+ (inactive-descriptions :layered-accessor attribute-inactive-descriptions
+ :initarg :deactivate
+ :initform nil
+ :layered t
+ :special t)))
+
+(define-layered-method attribute-active-p :around (attribute)
+ (let ((active? (call-next-method)))
+ (if (eq :when active?)
+ (not (null (attribute-value attribute)))
+ active?)))
+
+(define-layered-method attribute-label-formatter :around (attribute)
+ (or (slot-value attribute 'label-formatter)
+ (attribute-value (find-attribute (attribute-description attribute) 'label-formatter))
+ (error "No Formatter .. fool!")))
+
+(define-layered-method attribute-value-formatter :around (attribute)
+
+ (or (slot-value attribute 'value-formatter)
+ (attribute-value (find-attribute (attribute-description attribute) 'value-formatter))
+ (error "No Formatter .. fool!")))
+
+
+
+(define-layered-method attribute-object ((attribute standard-attribute))
+ (if (slot-boundp attribute 'object)
+ (call-next-method)
+ (described-object (attribute-description attribute))))
+
+
+(define-layered-function attribute-value-using-object (object attribute))
+(define-layered-function (setf attribute-value-using-object) (value object attribute))
+
+(define-layered-method attribute-value ((attribute standard-attribute))
+ (attribute-value-using-object (attribute-object attribute) attribute))
+
+(define-layered-method attribute-value-using-object (object attribute)
+ (let ((fn (handler-case (attribute-function attribute)
+ (unbound-slot () nil))))
+ (if fn
+ (funcall fn object)
+ (slot-value attribute 'value))))
+
+(define-layered-method (setf attribute-value) (value (attribute standard-attribute))
+ (setf (attribute-value-using-object (attribute-object attribute) attribute) value))
+
+(define-layered-method (setf attribute-value-using-object) (value object attribute)
+ (error "No (SETF ATTRIBUTE-VALUE-USING-OBJECT) for ~A ~A and we are not editable"
+ object attribute))
+