I would like to consider allowing the mime-type to be set during processing, perhaps even as late as after endDocument().
No, that's against "Cocoon Way". I'd even say, *all* headers should be set *before* startDocument, during pipeline assembly & setup stages. What's happening in ResourceReader currently WRT headers should be fixed - IIRC there is either Bugzilla entry for this or an email in archive.
Vadim
