<PackageReference Include="System.Configuration.ConfigurationManager" Version="10.0.0-rc.1.25451.107" />

System.Configuration.ConfigurationCollectionAttribute

Declaratively instructs .NET to create an instance of a configuration element collection. This class cannot be inherited.
namespace System.Configuration { public sealed class ConfigurationCollectionAttribute : Attribute { public Type ItemType { get; } public string AddItemName { get; set; } public string RemoveItemName { get; set; } public string ClearItemsName { get; set; } public ConfigurationElementCollectionType CollectionType { get; set; } public ConfigurationCollectionAttribute(Type itemType); } }