1. 繼承System.Exception
2. class名稱加上後置詞Exception
3. make exceptions runtime serializable
4. 至少提供下列幾個建構子

public class SomeException: Exception, ISerializble{
    public SomeException();
    public SomeException(string message);
    public SomeException(stirng message, Exception inner);
    
    //序列化需要
    protect SomeException(SerializationInfo info, StreamingContext context);
}

5. override ToString 提供安全敏感的錯誤內容(security-sensitive infomation)
6. 將security-sensitive infomation存成private狀態，確保趾有受信任的程式可以get