private void ExportCollada_NodeSub_BindMaterial(XmlWriter xml, params uint[] materialId) {
xml.WriteStartElement("bind_material");
xml.WriteStartElement("technique_common");
foreach (var materialName in materialId.Select(u => Materials.Values.ElementAt((int)u).Name)) {
xml.WriteElement("instance_material",
"symbol", $"{materialName}-material",
"target", $"#{materialName}-material");
}
xml.WriteEndElement(); // technique_common
xml.WriteEndElement(); // bind_material
}