Iterate over containerList with JSTL

According to the draft version of the template developer documentation I 
tried to use the JSTL expression 

- ${currentSite.allContainerLists[partnerContainer]}

but I get an error:
An error occurred while evaluating custom action attribute "items" with 
value "${currentSite.allContainerLists[partnerContainer]}": Unable to find 
a value for "allContainerLists" in object of class 
"org.jahia.data.beans.SiteBean" using operator "." (null)

It looks like it has not been implemented according to the proposal. I 
would like to iterate over a container list and display the fields of the 
containers by simplay using the JSTL tags <c:forEach> and <c:out>. Is it 
already possible?

Greetings,
Benjamin Papez