In the API docs, it is said that it's possible to use "location" for the domain nam in ordrer to update all domains for the user with one request. This would make updating several domains much easier, and with less manual configurtion.
However, I can't find how to define "location". So how do I define it?

When trying to search for posts containing this information, I used the search form in the top right corner. It opened a Google search!
Is there a way to search only inside the forum, and insite the current theme in the forum?

You can assign location names to your domain names in the control panel. If you log into the control panel->DDNS Services->Yourdomainname.com, you will see a 'Location' field where you can define the location name.

We are working on a search function to search only the forum and we hope to have this feature released soon.

Great! Thanks!

is location renamed to group?

Yes, evidently.