public HelpModel getHelpModel() {
		if (ui == null) {
			return null;
		}
		return ui.getHelpModel();
	}
A custom Table of Contents view that we specify in our JavaHelp xml documents.  This view 
lets us install custom renderers and custom tree items for use by those renderers.  These
renderers let us display custom text defined by the TOC_Source.xml files.  We also add some
utility like: tooltips in development mode, node selection when pressing F1.
Ghidra/Framework/Help/src/main/java/help/CustomTOCView.java