Well, I want to implement some Collapsible NSBox'es which will be able to stack up vertically, without margin. I have been watching the Reducer.app sample code, and it's actually the thing I'd like to have. My Collapsible Box class is working properly. It resizes the frame using NSAnimation nicely but there the problem begins: I have some more Collapsible NSBox'es below the perticular Collapsible NSBox, and I want them to stay just below the perticular NSBox, without margin. Now it just stays where I initially set it's frame origin to, which is not quite right because the NSBox above it became less in height. Since Leopard doesn't support palettes anymore, I can't open the Reducer's .nib file. I can't really get into the way Apple did do this and I've been searching for quite a long time now, but nothing found yet. I think it's possible to do this without an additional amount of code, since I can't find any of this this in Apple's example. Thanks in Advance! Some images to make it more clear: All Opened: Good Some Collapsed: Problem, the 'End Date' box needs to be below the 'Start Date' box, without margin.