The mediawiki supports fulltext-search. The limitations of this feature of mediawiki are that it indexes only words longer than 3 characters. If you want to search for shorter words (1-3 chars) then a known workaround is to use google. Just enter your search items in the form and it will automatically search within wiki.archlinux.org.
Of course, you can do the same manually:
your search items site:wiki.archlinux.org
This works fine, but it is not live. google is indexing the archwiki every 1-3 days.