--- a/CharacterEncoderImplementations__TwoByteEncoder.st	Thu Jan 26 12:51:57 2017 +0100
+++ b/CharacterEncoderImplementations__TwoByteEncoder.st	Thu Jan 26 12:54:19 2017 +0100
@@ -34,10 +34,24 @@
  other person.  No title to or ownership of the software is
  hereby transferred.
 "
+!
+
+documentation
+"
+    abstract superclass of all two-byte encoders
+"
 ! !
 
 !TwoByteEncoder class methodsFor:'queries'!
 
+isAbstract
+    "Return if this class is an abstract class.
+     True is returned here; false for subclasses.
+     Abstract subclasses must redefine this again."
+
+    ^ self == CharacterEncoderImplementations::TwoByteEncoder
+!
+
 maxCode
     ^ 16rFFFF 
 !