XML_Serializer and creating multi-level XML

How can you use XML_Serializer to generate XML with multiple levels ? XML_Serializer seems really useful for single level XML docs like: <parent> <child/> <child/> <child/> </parent How can I get XML_Serializer to do something like the below ? <parent> <child> <child/> <child> <child/> <child/> </child> </child> </parent> Or, is there something pre-existing that is better than XML_Serializer for multi-level XML ? I have built my own function to do this, but it is quite ugly and not as easy to reuse as I would like. many thanks My own query result looks similar to: playlist_id, media_id

1                , 1
1                , 2
1                , 3
2                , 1
2                , 5
3                , 10

And this is what I need XML_Serializer to generate: <query> <playlists> <playlist> <meta><id>1</id></meta> <content> <spot><id>1</id></spot> <spot><id>2</id></spot> <spot><id>3</id></spot> </content> </playlist> <playlist> <meta><id>2</id></meta> <content> <spot><id>1</id></spot> <spot><id>5</id></spot> </content> </playlist> <playlist> <meta><id>3</id></meta> <content> <spot><id>10</id></spot> </content> </playlist> </playlists> </query>