Hi Peter,I tried to perform this transformation with��RewriteTool��and got the same DNU.����However when I tried to execute it I was met with DNU OrderedCollection>>parent:It seems that the @first/@second part are not matched properly.Actually they are matched properly, because if you try to put in transformation part, for example, {``@first.``@second} everything works fine.����Any way to fix this? Or am I doing it wrong?I believe you are doing everything just fine. However, it is definately the problem of RBParseTreeRewriter or something related to it.��Try to execute following code in playground and you will get the same DNU:| rewriter |rewriter := RBParseTreeRewriter new replace: '| base |base := {(#Department->{``@first.``@second})}' with: '| base |base := {#Department -> (Array with: ``@first with: ``@second)}'.(rewriter executeTree: (RBParser parseRewriteExpression: '| base |base := {(#Department->{(1 @ 255).(Color lightMagenta)})}'))ifTrue: [ rewriter tree asString inspect ].This code does exactly the same that RewriteTool should do when you put all the parts into it.��Thus, I think, it is not a problem with the tool.Cheers,Mark