EDIT: https://sites.google.com/a/chromium.org/dev/tab-to-search
Basically I can type the first few characters of a domain until it autocompletes, then hit tab, then enter a search term which is submitted to that site's own search form, which chrome picked up when I went to the site, using various heuristics.
(While writing this I realized I didn't actually remember the exact domain Wikipedia and Wiktionary used... so I ran a "test" search on both.)
EDIT: https://sites.google.com/a/chromium.org/dev/tab-to-search
Basically I can type the first few characters of a domain until it autocompletes, then hit tab, then enter a search term which is submitted to that site's own search form, which chrome picked up when I went to the site, using various heuristics.