Currently to search on the wiki, you need to enter a search, hit enter, then edit the query to certain documents, having to start typing out "phriction", then re-submitting the query. It's an annoying mix of mouse & keyboard movements.
Even if I first select Phriction, there is no phriction-specific search field (that i've found).
Secondary motivation: I like to use chrome with custom search engines so I can quickly submit a search without loading the home page first. There is no url in which I can insert a search query (e.g. https://secure.phabricator.com/search/query/wiki/%s). If this were present, I wouldn't care about clicking around.