示例XML文件：
<?xml version="1.0" encoding="utf-8" ?>
<!— This is list of employees —>
<employees>
<employee employeeid="1">
<firstname>Nancy</firstname>
<lastname>Davolio</lastname>
<homephone>(206) 555-9857</homephone>
<notes>
<![CDATA[includes a BA in psychology from Colorado State University in
1970. She also completed "The Art of the Cold Call." Nancy is a member of
Toastmasters International.]]>
</notes>
</employee>
<employee employeeid="2">
<firstname>Andrew</firstname>
<lastname>Fuller</lastname>
<homephone>(206) 555-9482</homephone>
<notes>
<![CDATA[Andrew received his BTS commercial in 1974 and a Ph.D. in
international marketing from the University of Dallas in 1981. He is fluent
in French and Italian and reads German. He joined the company as a sales
representative, was promoted to sales manager in January 1992 and to vice
president of sales in March 1993. Andrew is a member of the Sales
Management Roundtable, the Seattle Chamber of Commerce, and the Pacific
Rim Importers Association.]]>
</notes>
</employee>
<employee employeeid="3">
<firstname>Janet</firstname>
<lastname>Leverling</lastname>
<homephone>(206) 555-3412</homephone>
<notes>
<![CDATA[Janet has a BS degree in chemistry from Boston College (1984).
She has also completed a certificate program in food retailing management.
Janet was hired as a sales associate in 1991 and promoted to sales
representative in February 1992.]]>
</notes>
</employee>
</employees>
1、在XML文档的元素间移动(Moving Between Elements)
五个基本方法：
ReadSubTree()方法：读取当前节点的子节点并返回XMLReader实例的一个子树。当你解析一个较大的XML文件，但是只希望处理其中的少部分数据的时候，这个方法非常有效。
作用示意如下图：
ReadToDescendant()：
ReadToFollowing()
ReadToNextSibling()
