[Inkscape-user] use, xlink:href, and external svg

I have a group of SVG documents which have a lot of objects in common; what I'd like to do is have a 'library' document which contains defs of those objects and then reference them in the other documents instead of repeating them umpteen times.

I thought that I could achieve that by putting objects in the <defs> part of my library document, e.g.,

<defs> <rect id="somerect" ... /> </defs>

and then referencing the objects elsewhere like this:

<use xlink:href="lib.svg#somerect" ... />

This seems not to work with Inkscape. (It does seem to work with Batik, but not if the href URL is relative.) Am I doing this incorrectly or is it unsupported?