Custom contentclass layouts currently must be implemented in <contentclass>:portlet.tml. This typically includes <tml:[hdb:content:portlet@base]> with custom body and other options.
my custom implementation ...
The problem with this is, that this tml will also included in edit and new mode. The hdb:content:portlet@base however will ignore all options. If the body is complex this is a waste of resources.
We now support <contentclass>:render.tml that is only included in view mode.