I would really like to limit some of my s earches to sites at universities, i.e. to xxx.edu sites. I think that this must be possible using a search set but I can’t see how.
The problem is that I don’t want to just search Harvard and Oxford but also UCLA, Berkeley etc. so entering each site individually is not a good solution.
One possibility is to create one or more dedicated plugins (just select File > New Plugin… and set the URL to .edu or xyz.edu). Finally, to use multiple plugins at once, create a new search set and enable all of them in the “Plugins” tab.
The .at restriction is only applied to the plugin and its search results but your search set is probably following links and the restriction is not applied to these links anymore.
Therefore I’d suggest to disable following of links and to increase the number of plugin results instead.