<PackageReference Include="System.Configuration.ConfigurationManager" Version="4.7.0-preview1.19504.10" />

SettingsGroupNameAttribute

public sealed class SettingsGroupNameAttribute : Attribute
Specifies a name for application settings property group. This class cannot be inherited.
namespace System.Configuration { [AttributeUsage(AttributeTargets.Class)] public sealed class SettingsGroupNameAttribute : Attribute { private readonly string _groupName; public string GroupName => _groupName; public SettingsGroupNameAttribute(string groupName) { _groupName = groupName; } } }