@Override
			public void mouseEntered(MouseEvent e) {
				// show a raised border, like a button (if the window is not already visible)
				if (tabPanel.isListWindowShowing()) {
					return;
				}

				setBorder(hoverBorder);
				setOpaque(true);
			}
Component displayed when not all tabs fit on the tab panel and is used to display a popup
list of all tabs.
Ghidra/Framework/Docking/src/main/java/docking/widgets/tab/HiddenValuesButton.java