Hi Casey,
For read-write access to XML data in Zope I would suggest looking at ParsedXML. I saw a message on the list saying it is not properly supported at the moment? However, I'll have a look at it.
If you are talking about megabytes (or hundreds of kb) of XML attached to a single object, separate file objects would probably be a good idea. You could make the content object folderish so that it can contain several files, one for the content and one (or more) for the metadata. Well, it will usually be a couple of pages . Hundreds of kb is probably a pessimistic maximum.
If you do have tons of XML to attach to a document, you'll also need to consider how you are going to work with it. Parsing such giants would be an expensive operation, so you would want to do it as seldom as possible. This XML will be transformed dynamically for presentation purposes. Further, other programs should be able to work with it, so they must be able to somehow access/download this XML.
I'll take a look at ParsedXML. But at the moment I favor your 'folderish object' idea as it seems to be easily extensible. It could be a simple product that knows how to render its contents etc. Thanks for your ideas, Lars