namespace System.Text
{
    [DefaultMember("Chars")]
    public sealed class StringBuilder : ISerializable
    {
        [EditorBrowsable(EditorBrowsableState.Never)]
        [InterpolatedStringHandler]
        public struct AppendInterpolatedStringHandler
        {
            public void AppendFormatted(ReadOnlySpan<char> value);
        }
    }
}