HM_SET_ACTIVE_WINDOW - Syntax

This message allows the application to change the window with which the Help Manager communicates and the window to which the help window is to be positioned.

param1
     HWND   hwndActiveWindow    /*  The handle of the window to be made active. */

param2
     HWND   hwndRelativeWindow  /*  The handle of the window next to which the help window is to be positioned. */