This page embeds the WYSIWYG Markdown editor in its own interface, the way an app such as the Journal embeds an editor. It uses a custom page fragment (example-ui.html.fragment) instead of the standard File, Desktop and Actions bar, saves automatically, and shows a live word count. The full guide is on the editor's own page under "Embedding in your own app".
Files: page.js (the StandaloneEditor configuration), example-ui.html.fragment (the custom interface) and example.md (the document being edited).