C# generic serialization utility class

Question

I have an existing class for serializing and deserializing objects to/from XML. It's a generic class with a single type parameter T whose only constraint is where T : IXmlSerializable. However, I want to still be able to use this class on classes that do not implement IXmlSerializable but have the [Serializable] attribute. How could I go about doing this?

From my generic class:

public static class XmlSerializationUtils<T> where T : IXmlSerializable
{
    public static T DeserializeXml(XmlDocument xml) { ... }
    public static XmlDocument SerializeToXml(T toSerialize) { ... }
}

I found this discussion but there was no solution given, just that I can't do where T : Serializable. Trying to do where T : SerializableAttribute makes Visual Studio say "Cannot use sealed class 'System.SerializableAttribute' as type parameter constraint".

Edit: based on Stephen's answer, I removed the constraints on XmlSerializationUtils<T> and added this static constructor:

static XmlSerializationUtils()
{
    Type type = typeof(T);
    bool hasAttribute = null != Attribute.GetCustomAttribute(type,
        typeof(SerializableAttribute));
    bool implementsInterface =
        null != type.GetInterface(typeof(IXmlSerializable).FullName);
    if (!hasAttribute && !implementsInterface)
    {
        throw new ArgumentException(
            "Cannot use XmlSerializationUtils on class " + type.Name +
            " because it does not have the Serializable attribute " +
            " and it does not implement IXmlSerializable"
        );
    }
}

Answer 1

You can check to see if a type is serializable using the IsSerializable property of the Type of the object.

myObj.GetType().IsSerializable

As mentioned, this isn't possible to add as a generic constraint, but would most likely be checked in a constructor.