This WPF code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace TestDict28342343
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();

            Dictionary<string, string> variableNamesAndValues = 
                new Dictionary<string, string>(StringComparison.InvariantCultureIgnoreCase);

        }
    }
}

gives me the error:

The best overloaded method match for 'System.Collections.Generic.Dictionary.Dictionary(System.Collections.Generic.IDictionary)' has some invalid arguments

Yet I find this code example everywhere such as here and here.

How can I define a Dictionary whose keys are case-insensitve?