[flossball]

It is the same as site:domain.name in google and most other search engines. You can add that at the end or beginning of the search string.

[groovybits]

you can also do:

!site <domain> <search string>

ex:

!site news.ycombinator.com duckduckgo

equates to:

site:news.ycombinator.com duckduckgo