Solution: 'XmlDocument' could not be found in Windows Store application code

When I added XmlDocument class to the code of my Windows Store (Windows 8 RT) application, I got the following error:

The type or namespace name 'XmlDocument' could not be found (are you missing a using directive or an assembly reference?)

Adding using System.Xml; directive did not help...

Solution: add using Windows.Data.Xml.Dom; directive:

using Windows.Data.Xml.Dom;
...
var xmlDocument = new XmlDocument();