OpenSearch is a relatively obscure topic that I’ve only crossed a few times, here is the premise.
A simple tag can be added to your content, in this case HTML, but a feed can also contain this element.
<link rel="search" href="http://www.giantgeek.com/opensearchdescription.xml" type="application/opensearchdescription+xml" title="giantgeek.com" />
That link refers to a file that resembles the one below, in it you can specify the URL to the search facilities on a website, or as in the case below, use the parameters for a Google search of your website.
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE OpenSearchDescription>
<OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/" xmlns:moz="http://www.mozilla.org/2006/browser/search/">
<ShortName>GiantGeek.com</ShortName>
<Description>Use Google to search our web site.</Description>
<InputEncoding>UTF-8</InputEncoding>
<Tags>giantgeek skotfred</Tags>
<Contact>[email protected]</Contact>
<Image width="16" height="16" type="image/x-icon">http://www.giantgeek.com/favicon.ico</Image>
<!-- NOTE: this uses Google, you can give your own search url instead -->
<Url type="text/html" method="GET" template="http://www.google.com/search?q=site:giantgeek.com {searchTerms}"/>
<Url type="application/opensearchdescription+xml" rel="self" template="http://www.giantgeek.com/opensearchdescription.xml"/>
</OpenSearchDescription>
Many modern browsers that provide a ‘search box’ in the browser interface, can then add the capability to perform a search of your website even when the user is not there already.
REFERENCES and Additional Reading: