I've been considering implement W3C XML Schema(WXS) but put it off because of the enormous amounts of work it requires(largely because of how the specs are written) and that I hadn't found any easy way to assess whether I've implemented it correctly. But perhaps this has changed with this test suite? Can one rely on this test suite for assessing how well ones validator will cope in the wild, or how crucial is it to build a complementary test collection?