a. If an object which is an element of the inner sequence has an attribute outer_item.
sure. The responsible programmer then has to use another prefix. Obviously.
Lets put it in a context... suppose the example dtml was part of a search results page on www.zope.org. The element of the sequence might be one of my HOWTOs. I am free to add any property to my HOWTOs. Therefore I can break the dtml if I know what prefix it is using, by adding a property with the appropriate name. Everything is fine if you are happy with level of robustness, but please remind me never to trust important data to your application.
b. If anything in the acquisision context of an element of the inner sequence has an attribute outer_item.
the same like a but only if the programmer wants to use the other element instead of the sequences.
Ahh - I not sure if youve missed the point. The dtml will use attributes from elements of the inner sequence or it acquisition context, in preference to those of the sequence, whether the programmer wants it or not.