// Base class with string Value and [XmlText]
public partial class CodeType {
    [XmlText]
    public string Value { get; set; }
}

// Derived class with EnumValue adapter property
public partial class TransConfirmationCodeType : CodeType {
    [XmlIgnore]
    public TransConfirmationCodeTypeEnum? EnumValue {
        get {
            if (Enum.TryParse(typeof(TransConfirmationCodeTypeEnum), Value, true, out var result))
                return (TransConfirmationCodeTypeEnum)result;
            return null;
        }
        set {
            Value = value?.ToString();
        }
    }
}

// Enum type for strongly-typed access
public enum TransConfirmationCodeTypeEnum {
    Always, Never, OnError
}

// Set using strongly-typed enum
var instance = new TransConfirmationCodeType();
instance.EnumValue = TransConfirmationCodeTypeEnum.Always;
// Value is automatically set to "Always"

// Read as strongly-typed enum
instance.Value = "Never";
var enumValue = instance.EnumValue; // Returns TransConfirmationCodeTypeEnum.Never

// Handle invalid values gracefully
instance.Value = "Invalid";
var invalid = instance.EnumValue; // Returns null