public interface IRuleMetadata
{
    [DefaultValue(0)]
    int ExecutionOrder { get; }
}
 
[AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = false)]
public class RuleAttribute : ExportAttribute, IRuleMetadata
{
    public RuleAttribute(int executionOrder)
        : base(typeof(IRule))
    {
        this.ExecutionOrder = executionOrder;
    }
 
    public int ExecutionOrder { get; set; }
}
 
[Rule(2)]
public class DateDiscountRule : IRule
{
    public void Execute(IOrder order)
    {
        if (DateTime.Now.Month == 2)
        {
            order.Price -= 100;
        }
    }
}
 
[ImportMany(typeof(IRule))]
public IEnumerable<Lazy<IRule, IRuleMetadata>> Rules { get; set; }