You can save the document and reopen it later just like in any other program. You might not be able to reproduce the graph validity error anymore because we fixed the specific bug you encountered. The input hints bar at the bottom shows what buttons you can press in any context, but that's a good idea to mention it in upcoming tutorials because I've noticed that users tend to ignore it. Hover tooltips and the app menu also both display shortcuts, which are worth pointing out in future tutorials as well. Thanks for that suggestion.