DocumentSet docs,
	public Sequence eval(		DocumentSet docs,		Sequence contextSequence,		Item contextItem)		throws XPathException {		if (contextItem != null)			contextSequence = contextItem.toSequence();		if(getArgumentCount() == 1)			contextSequence = getArgument(0).eval(docs, contextSequence);		if(contextSequence.getLength() == 0)			return StringValue.EMPTY_STRING;		return contextSequence.convertTo(Type.STRING);	}