A9.com > OpenSearch: "OpenSearch is a collection of technologies, all built on top of popular open standards, to allow content providers to publish their search results in a format suitable for syndication. You can see how this works on A9.com.
Many sites today return search results as a tightly integrated part of the website itself. Unfortunately, those search results can't be easily reused or made available elsewhere, as they are usually wrapped in HTML and don't follow any one convention. OpenSearch offers an alternative: an open format that will enable those search results to be displayed anywhere, anytime. Rather than introduce yet another proprietary or closed protocol, OpenSearch is a straightforward and backward-compatible extension of RSS 2.0, the widely adopted XML-based format for content syndication."