[Zope] what to put into DateIndexes?

hi! short question: what do i have to "put into" dateindexes? i tried to feed them with DateTime instances, ints, floats, strings - to no avail! the index list of the catalog shows "# objects: 0", though i have some objects in it, maybe you'd like to see the following screenshot: http://apis-intern.com/DateIndex.png - the rightmost colum shows what i've tried to put in there, the empty columns were initialized with DateTime instances, which don't show up at all here... plz help - i couldnt even find something about this trivial issue in the zopebook or elsewhere, they just show how dateindex hast to be queried... regards, juergen herrmann