The MulitpleSelection browser looks interesting (sort of like the tabbed browser in VisualWorks), but I don't quite understand its behaviour and what method it decides to show in which pane when you move around or save changes.
I'm actually right now working on a documentation for this browser, it should be finished soon.
I have now put this documentation online: http://scg.iam.unibe.ch/Research/Hermion (see in particular the wiki page linked).
If you still have any questions after reading this documentation, just tell me, then I will extend the doc.
David