public Sequence eval(StaticContext context, DocumentSet docs, Sequence contextSequence, Item contextItem) throws XPathException {
public Sequence eval(DocumentSet docs, Sequence contextSequence, Item contextItem) throws XPathException {
    public Sequence eval(StaticContext context, DocumentSet docs, Sequence contextSequence,    	Item contextItem) throws XPathException {		double sum = 0.0;		Sequence inner = getArgument(0).eval(context, docs, contextSequence, contextItem);		Item next;		for(SequenceIterator i = inner.iterate(); i.hasNext(); ) {			next = i.nextItem();			sum += ((NumericValue)next.convertTo(Type.NUMBER)).getDouble();		}		return new DoubleValue(sum);	}