Sorry, I didn't want to take too long explaining. But I already tried that way too, and it doesn't work either.
I saw a few pages on the net about referencing the repository, and that was one of the mentioned ways, but, that was only for using within the "Process Manager".
By the way, I tried specifying absolute file paths, like "C:\Fragments\Base.xdp", and they work.
I realize that relative "usehref" paths are more "robust" than absolute paths -- with relative paths we can open an xdp file both through the Workbench and through the Designer, as long as the relative position of files is maintained.
On the other hand, I really need to have pre-configured snippets of xfa in the Object Library, that have «usehref» attributes pointing to absolute positioned fragments in the repository, ready to drag-and-drop by our assumed "dummy" users.
My reasoning, in insisting to take this approach, is that it makes sense that such an absolute uri could be specified. Specially if, like me, one is trying to leverage the "inheritance" capabilities that the "usehref" supplies.
Unfortunately, apart from the aparent impossibility of specifying absolute repository uris, it seems that the Designer "doesn't like" «usehref>s that much. At the project I am working in, we experience constant designer crashes (the Visual C++ type ones included) while working with «usehref»ed objects. Things like «Copy&Paste» or, changing the order of «usehref»ed children, in the hierarchy, by «Drag&Drop> consistently cause the designer to crash. We don't know the exact pattern that causes the crashes, but can reproduce the error in certain identified documents.
I would be lying if I told you I wasn't expecting you to bring some light to these matters, as they have a significant importance on the mentioned project.
Thank you very much for you help