有关WM_WINDOWPOSCHANGING消息的问题

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我在研究WM_WINDOWPOSCHANGING消息时在delphi 6.0 的帮助中找到这样一段注解：
The WM_WINDOWPOSCHANGING message is sent to a window whose size, position, or place in the Z order is about to change as a result of a call to the SetWindowPos function or another window-management function.

WM_WINDOWPOSCHANGING
lpwp = (LPWINDOWPOS) lParam; // points to size and position data

Parameters

lpwp
Value of lParam. Points to a WINDOWPOS structure that contains information about the window's new size and position.

请问，LPWINDOWPOS类型在哪个单元中定义的
要在程序中使用LPWINDOWPOS,需要use 哪个单元？