From Joomla! Documentation

Adding support for new document renderers

New renderer types are added by creating a new file in the renderer directory under the document type directory with the same name as the renderer. For example, to add a document renderer type called "myrenderer" for document type "mytype", you would create the file /libraries/joomla/document/mytype/renderer/myrenderer.php. This file will contain the class definition for JDocumentRendererMytype which extends JDocumentRenderer. Look at the code for existing document renderers to see what needs to be done.

Chris Davenport 12:39, 17 April 2011 (CDT) Edit comment