XPath is far too concise. It needs an XML encoding. Something like PMML, where math looks like <DefineFunction name="frob" optype="continuous"> <Paramet

XPath is far too concise. It needs an XML encoding. Something like PMML, where math looks like <DefineFunction name="frob" optype="continuous"> <ParameterField name="x" optype="continuous"/> <Apply function="+"> <FieldRef field="x"/> <Constant>42</Constant> </Apply> </DefineFunction> I wish I were joking.