NodeSet result = ((NodeSet)lval).union((NodeSet)rval);
NodeSet result = lval.toNodeSet().union(rval.toNodeSet());
	public Sequence eval(Sequence contextSequence, Item contextItem) throws XPathException {		Sequence lval = left.eval(contextSequence, contextItem);		Sequence rval = right.eval(contextSequence, contextItem);		if(!(Type.subTypeOf(lval.getItemType(), Type.NODE) && Type.subTypeOf(rval.getItemType(), Type.NODE)))			throw new XPathException("union operand is not a node sequence");        NodeSet result = ((NodeSet)lval).union((NodeSet)rval);		return result;	}