'The pack URI of the .rels part corresponding to the current pack URI.
Only produces sensible output if the pack URI is a partname or the
package pseudo-partname \'/\'.'

@property
def rels_uri(self):

    rels_filename = ('%s.rels' % self.filename)
    rels_uri_str = posixpath.join(self.baseURI, '_rels', rels_filename)
    return PackURI(rels_uri_str)
