To Windows, controls are just specialized windows.

In ObjectWindows, TControl is derived from TWindow.

Control objects and window objects are similar in how they behave as child windows, and in how you create and destroy them. Standard controls differ from other windows, however, in that Windows handles their event messages and is responsible for painting them. Custom ObjectWindows controls handle these tasks themselves because the ObjectWindows control classes contain the code needed to paint the controls and handle events.

In many cases, you can directly use instances of control classes. However, sometimes you might need to create derived classes for specialized behavior. For example, you might derive a specialized list box class from TListBox called TFontListBox that holds the names of all the fonts available to your application and automatically displays them when you create an instance of the class.