The default way to persist a ProseMirror doc is JSON. There is a way to serialize that to Markdown via the prosemirror-markdown package, but not every node can

The default way to persist a ProseMirror doc is JSON. There is a way to serialize that to Markdown via the prosemirror-markdown package, but not every node can be represented as plain text. You can also use html without a non core package since each node has to define a toDOM and parseDOM method.