How to use a custom IXmlSerializable as an XmlAttribute?
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I implement `IXmlSerializable` for the type below which encodes which encodes and RGB color value as a single string:

	public class SerializableColor : IXmlSerializable
	{
		public int R { get; set; }
		public int G { get; set; }
		public int B { get; set; }
		
		public XmlSchema GetSchema()
		{
			return null;
		}

		public void ReadXml(XmlReader reader)
		{
			var data = reader.ReadString();
			reader.ReadEndElement();
			var split = data.Split(' ');
			R = int.Parse(split[0]);
			G = int.Parse(split[1]);
			B = int.Parse(split[2]);
		}

		public void WriteXml(XmlWriter writer)
		{
			writer.WriteString(R + " " + G + " " + B);
		}
	}

Since it's a single string, I wanted to store it as an attribute to save space. But as soon as I add the `[XmlAttribute]` to my property, I get the following exception:

> {"Cannot serialize member 'Color' of type SerializableColor. XmlAttribute/XmlText cannot be used to encode types implementing IXmlSerializable."}

Is there a way to make it work as an attribute too?