Ooops, I was doing a RenderTransform instead of a LayoutTransform. The latter is of course better as it keeps the control within its bounds and the content zooms, unfortunately so do the scroll bars and it looks a bit weird with big fat bars.
What I really need is to transform the "content" of the TreeView which from a copy of the template seems to be "<ItemsPresented/>", but getting the zoom behaviour on this is just too hard this afternoon. If I ever figure it out I'll let you know. I think that zooming parts of a WPF application is an important feature in the days of bigger screens, but web searches so far don't reveal any specific discussion of WPF techniques of doing this. Greg
