XmlReader is an abstract base class that provides an event-based, read-only, forward-only XML pull parser (I’ll discuss each of these terms shortly). XmlReader has three concrete subclasses, XmlTextReader, XmlValidatingReader, and XmlNodeReader, which enable you to read XML from a file, a Stream, or an XmlNode. You can also extend XmlReader to read other, non-XML data formats, and deal with them as if they were XML (you’ll learn how to do this in Chapter 4).

The base XmlReader provides only the most essential functionality for reading XML documents. It does not, for example, validate XML (that’s what XmlValidatingReader does) or expand XML entities into their respective character data (though XmlTextReader does). This does not mean that XML read from a text file cannot be validated at all; you can validate XML from any source by using the XmlValidatingReader constructor that takes an XmlReader object as a parameter, as I’ll demonstrate.

Here are those four terms I used to describe XmlReader again, with a little explanation.