@Override
			public boolean isEnabledForContext(ActionContext context) {
				Object contextObject = context.getContextObject();
				if (!(contextObject instanceof GTree)) {
					return false;
				}

				GTree gTree = (GTree) contextObject;
				if (gTree.getSelectionPaths().length != 1) {
					return false;
				}

				TreePath path = gTree.getSelectionPath();
				if (path == null) {
					return false;
				}

				GTreeNode node = (GTreeNode) path.getLastPathComponent();
				return (node instanceof CallNode);
			}
A variable used to restrict open-ended operations, like expanding all nodes or filtering.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/calltree/CallTreeProvider.java