This is a really important dialog. It ties together the two sides of news, reading and writing.
Then the river redirects to this domain, and the elements of the item you RT'd appear in its dialog box.
It remembers this domain in a cookie, so from then on, when you want to RT, it'll just take you to the blogging software.
I have to add a command that makes the river forget the domain, so you can connect to a different linkblog.
Also, if you want to use this technique in your static river, here's the URL to my template. You're free to use it as-is, or you can copy and modify it.
This feature is almost exactly like the POST button in Radio UserLand in 2002. It appeared next to an item in the aggregator. When you clicked it, the elements of the item would populate its built-in dialog for a new post. The difference is that in 2011, the two pieces are de-coupled. The aggregator and the linkblogging software are two different things, and don't even have to be made by the same people, and can be running on different servers.
A beautiful little bit of plumbing. Like putting a subway station in an airport.