Call MDI frame from SDI one.

[d2e8k]

hello!
I have application (SDI Frame).
I am trying to create window with MDI(!) frame by pressing button using the following code :
HWND hwnd = ::CreateWindowEx(
0, "EDIT", "Caption" ,
style,
rcFramePos.left, rcFramePos.top, rcFramePos.Width(), rcFramePos.Height(),
m_hWnd, NULL, NULL, 0);
::ShowWindow(hwnd, SW_SHOW);

Where/how should I define, that created window would have MDI frame?