Observe the following results for searching the text dictionary on Google:Notice that there is a custom search box at the bottom of the listing for dictionary.reference.com. Is there any documentation floating around that explains the criterion by which Google decides to display such a search box?
How did this website get a custom search bar listed under their search results?
google;site search
To follow up from the answer above, here's the official Google blog post about the feature:http://googleblog.blogspot.com/2008/03/search-within-site-tale-of.htmlThe key bit says: This feature will now occur when we detect a high probability that a user wants more refined search results within a specific site. Like the rest of our snippets, the sites that display the site search box are chosen algorithmically based on metrics that measure how useful the search box is to users.