[XPath] XPath Syntax

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XPath uses path expressions to select nodes or node-sets in an XML document. The node is selected by following a path or steps.

XPath使用路径表达式来选择XML文档中的节点或节点集。通过一个路径或steps（？？）来选择节点。

一 XML示例文档

<?xml version="1.0" encoding="UTF-8"?>

<book>

<title lang="en">Harry Potter</title>

</book>

<book>

<title lang="en">Learning XML</title>

</book>

</bookstore>

二节点选择

The most useful path expressions are listed below:

路径表达式：

Expression	Description
nodename	Selects all nodes with the name "nodename"
/	Selects from the root node
//	Selects nodes in the document from the current node that match the selection no matter where they are
.	Selects the current node
..	Selects the parent of the current node
@	Selects attributes

In the table below we have listed some path expressions and the result of the expressions:

下面表格中列出一些路径表达式以及表达式的结果：

Path Expression	Result
bookstore	Selects all nodes with the name "bookstore"
/bookstore	Selects the root element bookstore Note: If the path starts with a slash ( / ) it always represents an absolute path to an element!
bookstore/book	Selects all book elements that are children of bookstore
//book	Selects all book elements no matter where they are in the document
bookstore//book	Selects all book elements that are descendant of the bookstore element, no matter where they are under the bookstore element
//@lang	Selects all attributes that are named lang

三 Predicates(断言？？)

Predicates are used to find a specific node or a node that contains a specific value.

Predicates用来寻找一个特殊的节点，或者寻找含有特殊值的节点。

Predicates are always embedded in square brackets.

Predicates一直被封装在方括号中[]。

In the table below we have listed some path expressions with predicates and the result of the expressions:

含有断言的路径表达式以及结果的示例：

Path Expression	Result
/bookstore/book[1]	Selects the first book element that is the child of the bookstore element. Note: In IE 5,6,7,8,9 first node is[0], but according to W3C, it is [1]. To solve this problem in IE, set the SelectionLanguage to XPath: In JavaScript. xml.setProperty("SelectionLanguage","XPath");
/bookstore/book[last()]	Selects the last book element that is the child of the bookstore element
/bookstore/book[last()-1]	Selects the last but one book element that is the child of the bookstore element
/bookstore/book[position()<3]	Selects the first two book elements that are children of the bookstore element
//title[@lang]	Selects all the title elements that have an attribute named lang
//title[@lang='en']	Selects all the title elements that have a "lang" attribute with a value of "en"
/bookstore/book[price>35.00]	Selects all the book elements of the bookstore element that have a price element with a value greater than 35.00
/bookstore/book[price>35.00]/title	Selects all the title elements of the book elements of the bookstore element that have a price element with a value greater than 35.00

四选择未知节点(Selecting Unknown Nodes)

XPath通配符可用于选择未知的XML节点。

示例:

Path Expression	Result
/bookstore/*	Selects all the child element nodes of the bookstore element
//*	Selects all elements in the document
//title[@*]	Selects all title elements which have at least one attribute of any kind

五选择多条路径(Selecting Several Paths)

By using the | operator in an XPath expression you can select several paths.

在XPath表达式中使用"|"连接符，可以选择多条路径。

示例：

Path Expression	Result
//book/title \| //book/price	Selects all the title AND price elements of all book elements
//title \| //price	Selects all the title AND price elements in the document
/bookstore/book/title \| //price	Selects all the title elements of the book element of the bookstore element AND all the price elements in the document