Drop the file here
Nothing has been worked on yet. Every document lands here, and the ones you save stay for good.
A document opens in the left panel, which is the one you last touched.
A saved document stays in the history for good, under its name.
The document is fetched by the browser, so the site it is on has to allow it.
The document is checked against the schema as it changes, and what does not answer it is listed under it. An empty schema checks nothing.