@Override
	Element toXML() {
		// this call will put all the basic info into the element
		Element element = super.toXML();

		// we now need to put the xml for the grouped vertices into the element
		for (VertexInfo info : vertexInfos) {
			Element vertexElement = info.toXML();
			element.addContent(vertexElement);
		}

		// user defined text to display in the vertex
		String escapedText = XmlUtilities.escapeElementEntities(userText);
		element.setAttribute(USER_TEXT_ATTRIBUTE, escapedText);

		// background color
		element.setAttribute(BACKGROUND_COLOR_ATTRIBUTE, encodeColor(backgroundColor));

		return element;
	}
Note: this class should be created along with a GroupedFunctionGraphVertex, as the info
needed by this class is still available then.  To create this class later will result in
missing information (for example, edges get removed when vertices are grouped and this info
object will collect edge information, but cannot do so if they have been removed from the 
graph).
Ghidra/Features/FunctionGraph/src/main/java/ghidra/app/plugin/core/functiongraph/graph/vertex/GroupedVertexInfo.java