Recently, Google officially launched the display algorithm Google Search Box just below sitelink website is topped 1 with a particular keyword in Google search results.
Through its understanding, Google will display the search box if your website if your website with integrated data Microdata markup format type website like this:
2 data segment highlighted above will help search bots to identify what is the search box on the website and the search box that formats the query as to how to display a form out sitelink and while searching it will apply query frame that search.
If you’re using WordPress, the more easier because now plugin SEO by Yoast has self adding the data types marked JSON-LD website, then you do not need to do anything if they are taking Yoast.
But why so easy to make that web display and web again?
As we have often said that Google’s algorithm is always mysterious and do not follow any rules to avoid abuse of the other sites algorithm to put the poor quality content on top.
Previously, there Sitelinks quite mysterious and now add Google Search Box is also no less mysterious because not always display sites. There are some very large sites, there is enough data marked but still not showing. while there are some sites that are little or not to process (such as your blog) does show a miraculous way.
However, according to their observations, almost a Google Search Box is shown only if Web sites have a backlink is the sub-page large format (link to as their photo) not show unilateral or displayed along the sitelink small.
Therefore, whether the website you have markup data types for search box or not, it does not matter to Google for displaying this. But I believe that, if the website you have the credibility, the amount mentioned (in other websites they mention your domain name) well with the construction of regular content will be the reason for Google to allow you to enjoy the special offers.