Status field and attribute declaration

ApprovalStatus.cs

public class AATimeRequestStatus
    {
        public const string OnHold = "H";
        public const string PendingApproval = "P";
        public const string Approved = "A";
        public const string Rejected = "R";

        public class onHold : BqlString.Constant<onHold>
        {
            public onHold() : base(OnHold)
            {
            }
        }

        public class pendingApproval : BqlString.Constant<pendingApproval>
        {
            public pendingApproval() : base(PendingApproval)
            {
            }
        }

        public class approved : BqlString.Constant<approved>
        {
            public approved() : base(Approved)
            {
            }
        }

        public class rejected : BqlString.Constant<rejected>
        {
            public rejected() : base(Rejected)
            {
            }
        }

        public class AATimeRequestStatusListAttribute : PXStringListAttribute
        {
            public AATimeRequestStatusListAttribute() : base(
                new string[] 
                { 
                    OnHold, 
                    PendingApproval, 
                    Approved, 
                    Rejected
                }, 
                new string[] 
                { 
                    "On Hold", 
                    "Pending Approval", 
                    "Approved", 
                    "Rejected" 
                })
            {
            }
        }
    }

//Use of attribute on status field decleration

        #region Status
        public abstract class status : BqlString.Field<status>
        {
        }
        [PXDBString(1, IsFixed = true)]
        [PXDefault(AATimeRequestStatus.OnHold)]
        [AATimeRequestStatus.AATimeRequestStatusList]
        [PXUIField(DisplayName = "Status")]
        public virtual string Status { get; set; }
        #endregion