xpah筛选节点出现异常。


<?xml version="1.0" encoding="UTF-8"?>
<svg xsi:schemaLocation="OMICRON_SVG_20010904.xsd" height="100%" viewBox="0 0 2656 1566" width="100%" fill="#C0C0C0" image-rendering="optimizeSpeed" PB:pid="" xlink:xid="" xmlns:svg="OMICRON_SVG_20010904" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:PB="urn:osisoft-com-pb" xmlns:PBI="urn:osisoft-com-interface" xmlns:PBD="urn:osisoft-com-data" xmlns:xsi="http://www.w3.org/1999/XMLSchema/instance">
  <defs>
    <PBD:TagUses tag="\\1.1.1.1\aaa.aa" PB:BO="PWSPIEventsBO.cBOEvents">
      <PBI:Symbol name="Ellipse9_MS" PB:Type="3" PB:Parent="Ellipse9"/>
    </PBD:TagUses>
    <PBD:TagUses tag="\\1.1.1.1\bbb.bb" PB:BO="PWSPIEventsBO.cBOEvents">
      <PBI:Symbol name="TagBg2_MS" PB:Type="2" PB:Parent="TagBg2"/>
      <PBI:Symbol name="Value3" PB:Type="7"/>
    </PBD:TagUses>
  </defs>
</svg>            XmlDocument xmldoc = new XmlDocument();
            xmldoc.Load(Server.MapPath("1.xml"));
            string xPathExpression = "/svg/defs/PBD:TagUses"; //这样写会引发XPathException异常。描述为：需要命名空间管理器或 XsltContext。此查询具有前缀、变量或用户定义的函数。
            string xPathExpression = "/svg/defs/PBD:TagUses"; //这样可以
            XmlNodeList nodelist = xmldoc.SelectNodes(xPathExpression);
为什么呢？难道是Xpath中的“：”出现了问题？