return null;
switch(other.getType()) { case Type.YEAR_MONTH_DURATION: return other.plus(this); case Type.DAY_TIME_DURATION: return other.plus(this); default: throw new XPathException( "Operand to plus should be of type xdt:dayTimeDuration or xdt:yearMonthDuration; got: " + Type.getTypeName(other.getType())); }
	public ComputableValue plus(ComputableValue other) throws XPathException {		// TODO Auto-generated method stub		return null;	}