As with all bookmarklets, you install it by dragging it from the web page into the icon bar in your browser.
Now, with the browser open to this page, click on the bookmarklet and prepare to have your socks blown off!
The source of the page opens in the browser, in an outliner, where you can browse it and edit it. The editing doesn't save back to the server, yet -- but it will. (Of course only if you have permission to edit the document.)
Marc already had a web outliner called iJot. I showed him how Scripting2 embeds a link to the OPML source in every page. From there it was relatively easy to detect the OPML and open it.
BTW, this is how a bootstrap works.