There may be times when you want your ESL application to determine the window handle (HWND) that is passed to the stimulus initialization routine (using PostMessage). You can use the copy action statement with the handle of built-in function to copy the window handle of the stimulus DLL into an integer.

stimulus Important 

integer Hwnd

response to start

copy handle of "Important" to Hwnd

Hwnd now contains the same window handle that was passed to the stimulus initialization routine.