SpawnDetailAttribute.cs

using System;

[AttributeUsage(AttributeTargets.Field, AllowMultiple = false, Inherited = false)]
public class SpawnDetailAttribute : Attribute
{
    public string DetailKey
    {
        get { return _detailKey; }
    }

    string _detailKey = null;

    public SpawnDetailAttribute (string detailKey = null)
    {
        _detailKey = detailKey;
    }
}