Scoped search
Scoped search lets users limit the search to results from specific areas of the site (the search scope). In general, this is dangerous . Users often overlook the scope, or they think they are in a different site area than the one they are actually searching.
However, as websites continue to grow and offer multiple services in a single site, my attitude toward scoped search is changing. I now believe scoping can be sufficiently useful if you offer it in areas of the site that are both clearly delimitated and address specific problems.
If you choose to use scoped search, I recommend following a few basic rules:
Set the default search scope to "all" (search the entire site). When the user chooses a narrow search scope, explicitly state the scope at the top of the results page. Offer one-click access to enlarge the scope. It is especially important to give users a highly visible way of searching the entire site if their scoped search fails to return any results. If a search returns too many results, give users suggestions for limiting the scope.