[galaxy-dev] Data Collection collection_type list:list

Hi, I was wondering if creating data collection of collection_type="list:list" is possible? Because I can see only list, pair and list of pairs options available. Why I am asking this question is because I saw this snippet from cuffdiff tool which includes collection_type="list:list" as below. <when value="CONDITION_REPLICATE_LIST"> <param name="conditions" title="List of Conditions" type="data_collection" collection_type="list:list" /> </when> Thanks Anmol