--- a/DeviceHandle.st	Wed Feb 08 18:32:11 2017 +0100
+++ b/DeviceHandle.st	Fri Feb 10 11:17:50 2017 +0100
@@ -11,6 +11,8 @@
 "
 "{ Package: 'stx:libview' }"
 
+"{ NameSpace: Smalltalk }"
+
 Object subclass:#DeviceHandle
 	instanceVariableNames:'device drawableId gcId'
 	classVariableNames:''
@@ -53,6 +55,16 @@
 "
 ! !
 
+!DeviceHandle 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 == DeviceHandle.
+! !
+
 !DeviceHandle methodsFor:'accessing'!
 
 device