run in the browser."
            ```

            ```javascript; runnable
            return "Javascript can be, though. Click play!";
            ```

            Because it's just Markdown, and all the work is done by a script in the browser, it's really easy for users to create new notebooks from scratch. But you might not want to create from scratch, so...

            ## Every notebook is editable

            You might have noticed the little pencil icon in the top-right. Give it a poke! You'll find y