What is a Mode in the Windowing System?

"Mode" refers to "docking mode". A Mode is a place in a main window, a place between splitters. Separate "floating" window is also backed by Mode. Mode is usually visually represented by a tabbed container. Programmatically it is represented by the class org.openide.windows.Mode

Think of a Mode as synonymous with a one of the tabbed containers you see in the IDE's main window. The name "Mode" is historical, and a bit unfortunate. When you hear "Mode," think tabbed container and you'll be fine.

A Mode is not a GUI component. There is no legitimate programmatic way to fetch the component that represents a Mode on-screen, and the windowing system makes no guarantees about what that component is.

Modes can contain one or more TopComponents. They may be visible or non-visible at any given time.