Online Help says:
Dialog Properties: More Styles
Creates a dialog box that works well as a child window of another dialog box, much like a page in a property sheet. This style allows the user to tab among the control windows of a child dialog box, use its accelerator keys, and so on. Type: Bool. Default: False.
This is the complete information i've found about it. I have no idea how it works to display other dialogs as control in a modal dialog box.
a sample program would be fine.