It is using Saxon … or, at least, that’s what <factory name="net.sf.saxon.TransformerFactoryImpl"/> implies to me.
Will Saxon not run XSLT 1.0? I'd have thought it would.
How do we run XSLT 1 from ant? (In particular, from P5/antbuilder.xml. I tried "trax", but get a fatal “XSLT 1.0 compatibility mode is not available in this configuration”.)