现有一个xml文件：
<?xml version="1.0" encoding="utf-16"?>
<componentDocuments>
<componentDocument Version="1.0">
<header>
<flow ID="GOGOGO" nodeID="Begin" >
<fileName>xml/workflows/SignOnFlow.xml </fileName>
<declares />
<sequence outcome="" />
</flow>
<returnStack />
<index>1 </index>
</header>
</componentDocument>
</componentDocuments>
现在想把 <fileName>元素下对应的值xml/workflows/SignOnFlow.xml变为c:\AAA\xml\workflows\SignOnFlow.xml并更新到 <fileName>元素下，即变为新的xml文件：
<?xml version="1.0" encoding="utf-16"?>
<componentDocuments>
<componentDocument Version="1.0">
<header>
<flow ID="GOGOGO" nodeID="Begin" >
<fileName>c:\AAA\xml\workflows\SignOnFlow.xml </fileName>
<declares />
<?xml version="1.0" encoding="gb2312" ?>
<sites>
<site>
<name>.Net开发者园地</name>
<url>http://dotnet.aspx.cc</url>
<img&g ......
