this.cardinality = cardinality;
this.requiredCardinality = requiredCardinality;
	public CastableExpression(XQueryContext context, Expression expr, int requiredType, int cardinality) {		super(context);		this.expression = expr;		this.requiredType = requiredType;		this.cardinality = cardinality;		if (!Type.subTypeOf(expression.returnsType(), Type.ATOMIC))			expression = new Atomize(context, expression);	}