Some system DLL routines can manipulate windows on the display. To allow these routines to interact with ABL windows, every ABL user interface widget has the HWND attribute. This attribute contains the Windows handle to the window that contains the widget. You can pass this window handle as an integer value to a DLL routine using a LONG DLL parameter or a LONG location in a structure (MEMPTR) parameter.

CAUTION: When you pass an HWND to a DLL routine, that routine has complete control of a system window that ABL is using for its own widget management. This means that the DLL routine can modify the window's attributes and even destroy the window itself without ABL knowing about it. Such actions can cause unintended effects on your OpenEdge application.