[Zope] security with dtml-in next-batches variable

Why doesn't this work: <dtml-in expr="_.range(100)" size="10"> <dtml-if next-batches> <dtml-var expr="_['next-batches'][-1]['batch-start-index']"> </dtml-if> </dtml-in> (it results in Unauthorized, from line 168 in ZopeSecurityPolicy) However, I can dtml-in over next-batches: <dtml-in expr="_.range(100)" size="10"> <dtml-if sequence-end> <dtml-in next-batches mapping> <dtml-var batch-start-index> </dtml-in> </dtml-if> </dtml-in> (this works fine, but will be needlessly slower than just <dtml-var>ing the correct value.) Thanks, -Randy