Placeholder for 2.3 operations.

NTwain/Triplets/DGControl/DGControl.Capability.cs

@@ -124,5 +124,7 @@ namespace NTwain.Triplets
 			Session.VerifyState(4, 6, DataGroups.Control, DataArgumentType.Capability, Message.Set);
 			return PInvoke.DsmEntry(Session.AppId, Session.SourceId, Message.Set, capability);
 		}
+
+        //TODO implement SetConstraint
 	}
 }

NTwain/Triplets/DGControl/DGControl.XferGroup.cs

@@ -4,6 +4,8 @@ using NTwain.Values;
 
 namespace NTwain.Triplets
 {
+    // TODO: implement this
+
 	public sealed class XferGroup : OpBase
 	{
 		internal XferGroup(ITwainSessionInternal session) : base(session) { }

NTwain/Triplets/DGImage/DGImage.Filter.cs

@@ -0,0 +1,13 @@
+using NTwain.Data;
+using NTwain.Values;
+using System;
+
+namespace NTwain.Triplets
+{
+	public sealed class Filter : OpBase
+	{
+        internal Filter(ITwainSessionInternal session) : base(session) { }
+
+        //TODO: implement this
+	}
+}