The Google Search Appliance ships with a full-function — but no thrills — XSL template (XSLT) that we refer to as the ‘out of the box’ user interface.  It looks a little bit like google.com did a few years ago – lots of blue and white, and very few graphics.  But it does support all of the enterprise features that the GSA includes, such as Dynamic Navigation, Document Preview, Expert Search, and more.

You can think of the XSLT as a skin on top of the XML results that the GSA produces.  When you run a search, the GSA generates an XML document with your results, and then optionally applies an XSL template of your choice to that XML.  The XSLT converts the XML into HTML, and then the GSA’s web server delivers the HTML to your browser.