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.
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.