<PackageReference Include="System.Configuration.ConfigurationManager" Version="4.6.0-preview.19073.11" />

ConfigurationPropertyOptions

Specifies the options to apply to a property.
namespace System.Configuration { [Flags] public enum ConfigurationPropertyOptions { None = 0, IsDefaultCollection = 1, IsRequired = 2, IsKey = 4, IsTypeStringTransformationRequired = 8, IsAssemblyStringTransformationRequired = 16, IsVersionCheckRequired = 32 } }