When does Uri.CheckHostName() return UriHostNameType.Basic instead of UriHostNameType.Dns or UriHostNameType.Unknown?

Now the .NET Core is open source we can know for sure.

Just like Mono, it never returns UriHostNameType.Basic.

Link to source code

It occurred to me that I could just check the Mono source code to answer my question. Here is the CheckHostName method from https://github.com/mono/mono/blob/master/mcs/class/System/System/Uri.cs:

    public static UriHostNameType CheckHostName (string name) 
    {
        if (name == null || name.Length == 0)
            return UriHostNameType.Unknown;

        if (IsIPv4Address (name)) 
            return UriHostNameType.IPv4;

        if (IsDomainAddress (name))
            return UriHostNameType.Dns;             

        IPv6Address addr;
        if (IPv6Address.TryParse (name, out addr))
            return UriHostNameType.IPv6;

        return UriHostNameType.Unknown;
    }

It appears that UriHostNameType.Basic isn't used at all. Maybe the Microsoft implementation can return this value?