You can't make a child window exceed it's parents boundaries. That's not what a child window is supposed to do. According to your screenshot, you want to make a search field. (which is a pretty nice idea!
) I recommend you to subclass the chat window and move your PlusWnd when you receive a WM_SIZE (and eventually a WM_SIZING) message and change the positions of your child window based on the new window rectangle.
This may be tricky, so if you need help with it, PM me with your e-mail address and I'll try to help you out.
I'll have to do some research on how to subclass windows first myself too, but once we have a WM_SIZE message, it'll be easy to move the child window.
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