Sun's specification [JSR-168|http://www.jcp.org/aboutJava/communityprocess/review/jsr168/] is an API specification to be followed by Portlets, which are, loosely, "components" of a composite web application, each responsible for painting its own rectangle of the browser window. As of release 0.6.3 RSF features [RSFPortlet], producing a JAR enabling RSF applications to execute as portlets without code changes.