WordPress OpenSearch is a WordPress plugin. Help you to easy to add OpenSearch to your wordprss site.
Tutorial how to write this plugin : http://laptrinh.senviet.org/wordpress-plugin/viet-plugin-them-opensearch-vao-wordpress/