public Sequence eval(StaticContext context, DocumentSet docs, Sequence contextSequence, Item contextItem)
public Sequence eval(DocumentSet docs, Sequence contextSequence, Item contextItem)
	public Sequence eval(StaticContext context, DocumentSet docs, Sequence contextSequence, Item contextItem) 	throws XPathException {		if(contextItem != null)			contextSequence = contextItem.toSequence();		if(getLength() == 0)			throw new XPathException("unary expression requires an operand");		DoubleValue value = (DoubleValue)			getExpression(0).eval(context, docs, contextSequence).convertTo(Type.DECIMAL);		switch(mode) {			case Constants.MINUS :				value.setValue(-value.getDouble());				break;			case Constants.PLUS :				value.setValue(+value.getDouble());		}		return value;	}