This topic is included for completeness. For more detail see the source code located in the VC\atlmfc\src\mfc folder of your Visual Studio installation.
virtual void OnDrawExpandingBox(
CDC* pDC,
CRect rect,
BOOL bIsOpened,
COLORREF colorBox
);
Parameters
[in] pDC
[in] rect
[in] bIsOpened
[in] colorBox
Requirements
Header: afxvisualmanager.h