Portlets are web components--like servlets--specifically designed to be aggregated in the context of a composite page. Usually, many portlets are invoked to in the single request of a portal page. Each portlet produces a fragment of markup that is combined with the markup of other portlets, all within the portal page markup." (from the Portlet Specification, JSR 168)

The current PHP WSRP library is a full implementation of the WSRP customer written in PHP. It is based on the text of the Oasis wsrp primer 1.0 which is available at http://www.oasis-open.org/committees/download.php/10539/wsrp-primer-1.0.html