The portlet programming interface provides a mechanism to assist portlets when
the aggregated portal markup is an HTML or similar document that requires markup
for the document HEAD section to be written and HTTP headers to be
set before the render markup for each individual portlet is aggregated.
This mechanism is represented in the portlet API by the HeaderPortlet,
HeaderRequest, and HeaderResponse interfaces.
The HeaderRequest provides the portlet with information about
the request.
HeaderResponse, HeaderPortlet