Applies the specified pattern-matching operation to this node's context and returns the first matching node
返回第一个匹配的项
2.2.4 selectNodes
Applies the specified pattern-matching operation to this node's context and returns the list of matching nodes as IXMLDOMNodeList
符合条件的所有项。
2.2.5 getElementsByTagName
Returns a collection of elements that have the specified name
返回与元素名匹配的一个node的集合