Message reflection lets you handle messages for a control, such as WM_CTLCOLOR, WM_COMMAND, and WM_NOTIFY, within the control itself. This makes the control more self-contained and portable. The mechanism works with Windows common controls as well as with ActiveX controls (formerly called OLE controls).
Message reflection lets you reuse your CWnd-derived classes more readily. Message reflection works via CWnd::OnChildNotify, using special ON_XXX_REFLECT message map entries: for example, ON_CTLCOLOR_REFLECT and ON_CONTROL_REFLECT. Technical Note 62 explains message reflection in more detail.