Sean McGrath writes:

... "dtml-in" treats sequences of two element tuples specially ... You are right. This is to support the frequent case of iterating over item sequences.

There should be a "dtml-in" argument to switch off this special treatment. If I had your problem, I would go for such a solution (extending "dtml-in"). It should be easier than to work around the special treatment in DTML and it would help the Zope community as a whole. If you do not want to go this way, I would suggest to put a feature request into the Collector. Dieter