What algorithm does google use to make Chrome browser's address bar to act as a default search bar for many websites?

Question

I am wondering what algorithm does google use to make chrome browser's address bar to act as a default search bar for many websites like SO, Quroa etc. but not for facebook, metastackoverflow etc..

For example if you want to search for a topic in stackoverflow, you can do like this in chorme.

And the search results will directly take you to the stackoverflow page. i.e.

The same will happen if you choose to search quora.com also in chrome's address bar. But this won't happen if you search like facebook.com in the address bar and many other websites that have a search bar.

How is this happening? What algorithm does google use to make this happen?

Hope I am clear with my question? Any help would be appreciated.

Answer 1

This feature is powered by what is known as OpenSearch. It allows you to specify how queries are supposed to be formed when searching a website. You can read the documentation here: http://www.opensearch.org/Home

For example, StackOverflow has the following in their HTML source code:

<link rel="search" type="application/opensearchdescription+xml" title="Stack Overflow" href="/opensearch.xml">

If you then open the file /opensearch.xml you can see the following:

<?xml version="1.0" encoding="UTF-8" ?>
<OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/" xmlns:moz="http://www.mozilla.org/2006/browser/search/">
  <ShortName>Stack Overflow</ShortName>
  <Description>Search Stack Overflow: Q&amp;A for professional and enthusiast programmers</Description>
  <InputEncoding>UTF-8</InputEncoding>
  <Image width="16" height="16" type="image/x-icon">http://sstatic.net/stackoverflow/img/favicon.ico</Image>
  <Url type="text/html" method="get" template="http://stackoverflow.com/search?q={searchTerms}"></Url>
</OpenSearchDescription>

The most important part is the line that specifies the search term string in line 7.

Answer 2

Chrome uses search engines mechanism. It is described here how to use it http://support.google.com/chrome/bin/answer.py?hl=en&answer=95653&topic=14676&ctx=topic

Chrome automatically identifies search boxes and adds corresponding rules to search engines list. Maybe it's engine relies on document parsing. Hense a particular site may be added or not because of it's search box markup. https://superuser.com/questions/276069/google-chrome-automatically-adding-websites-to-my-list-of-search-engines

If you want to know about parsing algorithm, the only way i see is to dig through chrome sources

Also, you can edit search engine list manually.

PS: And it's not only chrome's feature, other browsers have similar things. Opera as an example http://tech.gaeatimes.com/index.php/archive/how-to-easily-use-manage-your-search-engines-in-opera-browser/