Sequence arg = getArgument(0).eval(context, docs, contextSequence); return arg.convertTo(Type.DECIMAL);
Sequence arg = null; if(getArgumentCount() == 1) arg = getArgument(0).eval(docs, contextSequence); else arg = contextSequence; if(arg.getLength() == 0) return DoubleValue.NaN; else return arg.convertTo(Type.DOUBLE);
	public Sequence eval(StaticContext context, DocumentSet docs, Sequence contextSequence,		Item contextItem) throws XPathException {		if(contextItem != null)			contextSequence = contextItem.toSequence();		Sequence arg = getArgument(0).eval(context, docs, contextSequence);		return arg.convertTo(Type.DECIMAL);	}