@Override
	public void processEvent(PluginEvent event) {
		if (event instanceof ProgramClosedPluginEvent) {
			ProgramClosedPluginEvent ev = (ProgramClosedPluginEvent) event;
			referenceHoverService.programClosed(ev.getProgram());
		}
	}
A plugin to show tool tip text for hovering over references in the listing.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/codebrowser/hover/ReferenceListingHoverPlugin.java