From Seo Wiki - Search Engine Optimization and Programming Languages
OpenSearch is a collection of technologies that allow publishing of search results in a format suitable for syndication and aggregation. It is a way for websites and search engines to publish search results in a standard and accessible format.
OpenSearch was developed by Amazon.com subsidiary A9 and the first version, OpenSearch 1.0, was unveiled by Jeff Bezos at the Web 2.0 conference in March, 2005. Draft versions of OpenSearch 1.1 were released during September and December 2005. The OpenSearch specification is licensed by A9 under the Creative Commons Attribution-ShareAlike 2.5 License.
OpenSearch consists of:
- OpenSearch Description files: XML files that identify and describe a search engine.
- OpenSearch Query Syntax: describe where to retrieve the search results
- OpenSearch RSS (in OpenSearch 1.0) or OpenSearch Response (in OpenSearch 1.1): format for providing open search results.
- OpenSearch Aggregators: Sites that can display OpenSearch results.
- OpenSearch "Auto-discovery" to signal the presence of a search plugin link to the user and the link embedded in the header of HTML pages
OpenSearch Description Documents list search result responses for the given website/tool. Version 1.0 of the specification only allowed one response, in RSS format; however, version 1.1 provides support for multiple responses, which may be in any format. RSS and Atom are the only ones formally supported by OpenSearch aggregators, however other types, such as HTML are perfectly acceptable.
Search engines and software that support OpenSearch
- Wikipedia suggests articles matching a typed-in entry with incremental find.
- Internet Explorer 7 and above, to integrate web search services with its search bar.
- Windows 7 and Microsoft Search Server to let users federate searches to web services via a centralized location. (Note that even if the Site does not support OpenSearch, through a service on the "Find More Providers" page, one can add a website with a search engine if "TEST" is searched and the URL of the search page contains "TEST".)
- Mozilla Firefox 2 and above implement OpenSearch, as well as a subset named MozSearch. MozSearch is not intended for web use, only for Firefox related projects. Extended features from MozSearch are usable in an OpenSearch file with an XML namespace prefix. Features specific to MozSearch include search suggestions, among others. 
- Google Chrome
- ↑ Ogbuji, Uche (July 24, 2007). "Introducing OpenSearch". xml.com. http://www.xml.com/pub/a/2007/07/20/introducing-opensearch.html.
- ↑ "Supporting search suggestions in search plugins" (HTML). Mozilla Developer Center. https://developer.mozilla.org/en/docs/Supporting_search_suggestions_in_search_plugins. Retrieved 2007-08-03.
- ↑ "OpenSearch search clients - Web browsers". opensearch.org. http://www.opensearch.org/Community/OpenSearch_enabled_search_clients. Retrieved 2009-12-24.
- OpenSearch.org – official website, including specifications
- Search2.net search engine supported OpenSearch queries.