--- a/GraphicsMedium.st	Wed Mar 07 18:06:48 2018 +0100
+++ b/GraphicsMedium.st	Wed Mar 07 18:06:56 2018 +0100
@@ -837,7 +837,12 @@
 !
 
 function:aSymbol
-    "set the drawing function if it has changed"
+    "set the drawing function if it has changed.
+     The argument is one of:
+            #copy,#copyInverted,#xor,#and,#andReverse
+            #andInverted,#or,#orReverse,#orInverted
+            #invert,#clear,#set,#noop,#equiv,#nand
+     Notice: not all graphicMedia support all functions"
 
     gc function:aSymbol
 !