What triggers Site Search below the sitelinks?

[designaweb]

A search for a certain travel related keyphrase in Google.co.uk returns "example.com" as the #1 result. It shows the title, snippet, and then a searchbox? (followed by the URL).

I've seen sitelinks, but does anyone have a clue what the appearance of this searchbox in the SERPS triggers?

[edited by: tedster at 7:34 pm (utc) on May 23, 2008]

[tedster]

It was first noticed back in March - see this discussion New Search Box Under Sitelinks [webmasterworld.com]. That thread has a number of specific examples - we don't usually allow example searches, however, and that policy will hold for this current duiscussion.

You see the results for a regular "keyword + site:example.com" search - not the site's internal site search. So what is the trigger? It seems to be another relatively complex algorithm. My guess is that it's based on the depth of the site involved, how often a given query for that site is followed by a revised query, howoften the search box gets used during a test period, and probably a good bit more.

Here's the official Google Blog post from March 5:

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.

[googleblog.blogspot.com...]