<PackageReference Include="NETStandard.Library" Version="2.0.0-preview2-25401-01" />

System.Xml.Serialization.XmlChoiceIdentifierAttribute

namespace System.Xml.Serialization { public class XmlChoiceIdentifierAttribute : Attribute { public string MemberName { get; set; } public XmlChoiceIdentifierAttribute(); public XmlChoiceIdentifierAttribute(string name); } }