This function retrieves the handle to the first control with the WS_TABSTOP style that precedes or follows the specified control.
HWND GetNextDlgTabItem( HWND hDlg, HWND hCtl, BOOL bPrevious );
[in] Handle to the dialog box to be searched.
[in] Handle to the control to be used as the starting point for the search. If this parameter is NULL, the function uses the last (or first) control in the dialog box as the starting point for the search.
[in] Boolean that specifies how the function is to search the dialog box. If this parameter is TRUE, the function searches for the previous control in the dialog box. If this parameter is FALSE, the function searches for the next control in the dialog box.
The window handle of the previous or next control that has the WS_TABSTOP style set indicates success. NULL indicates failure. To get extended error information, call GetLastError.