--- a/DisplayObject.st	Thu Feb 09 23:46:29 2017 +0100
+++ b/DisplayObject.st	Fri Feb 10 11:18:01 2017 +0100
@@ -75,6 +75,16 @@
     "Modified: 28.3.1997 / 16:40:44 / cg"
 ! !
 
+!DisplayObject class methodsFor:'queries'!
+
+isAbstract
+    "Return if this class is an abstract class.
+     True is returned here for myself only; false for subclasses.
+     Abstract subclasses must redefine this again."
+
+    ^ self == DisplayObject.
+! !
+
 !DisplayObject methodsFor:'ST-80 drawing'!
 
 displayOn:aDisplayMedium at:aPoint