Mini Google Search box within organic sitelinks

[Mobies]

I'm trying to find solid information on Google's criteria on showing a "mini Google search box" within sitelinks?

Example: if you type-in "wikipedia" on Google.com, a mini search box appears within the site links. This is for organic listing not paid listing.

The Google Support page on Sitelinks does not state any info on the mini google search box. http://support.google.com/webmasters/bin/answer.py?hl=en&answer=47334

[Martijn_Scheijbeler]

It looks like to me the criteria are that you need to be a big brand to get your own search box within the search results. It could be that these sites are hand picked. Search Engine Land covered this topic a couple of years ago. Read the article here.