A common dialog box sends the HELPMSGSTRING registered message to the window procedure of its owner window when the user clicks the Help button.
For Explorer-style Open and Save As dialog boxes, this message has been superseded by the CDN_HELP notification message.
MessageID = RegisterWindowMessage(HELPMSGSTRING);
hdlg = (HWND) wParam;
lpStruct = (LPVOID) lParam;
No return value.
You must specify the HELPMSGSTRING constant in a call to the RegisterWindowMessage function to get the identifier for the message sent by the dialog box.
When you create the dialog box, use the hwndOwner member of the initialization structure to identify the window to receive HELPMSGSTRING messages.
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Unsupported.
Header: Declared in commdlg.h.
Unicode: Defined as Unicode and ANSI messages.
Common Dialog Box Library Overview, Common Dialog Box Messages, CDN_HELP, CHOOSECOLOR, CHOOSEFONT, FINDREPLACE, OPENFILENAME, PRINTDLG, PAGESETUPDLG, RegisterWindowMessage