Window functions allow manipulation of source file windows. File buffers are displayed in source windows. An hwnd is typically a small integer value. An hwnd of hNil indicates an error.
The functions use window handle (hwnd) parameters. These are macro-level handles to open source file windows. Note that a macro hwnd is similar in concept, but is not exactly the same as a window handle HWND in the Microsoft Windows API.
Each source window has a selection in it, which describes what characters are selected. See GetWndSel (hwnd) for more information.
In some functions, a window handle (hwnd) can also represent a handle to a system level window, such as the application window. System level windows do not contain a file buffer, or a selection. The GetApplicationWnd function returns a handle to the Source Insight application window.