I think you are using the wrong function for what you are trying to do. Use eZContentObjectTreeNode::subTree or instead. Łukasz wrote a nice blog article in which you can find a few examples: http://serwatka.net/en/blog/fetching_ez_publish_content_objects_with_php.
The conditions parameter to eZPersistentObject::fetchObjectList is documented well with Doxygen (the API docs are at http://pubsvn.ez.no/doxygen/3.9/html/index.html ).