Tutorials 参考 练习 Menu
Paid Courses

XML 教程

XML主页 XML简介 XML使用方法 XML Tree XML语法 XML元素 XML属性 XML命名空间 XML显示 XML HttpRequest XML解析器 XML DOM XML XPath XML XSLT XML XQuery XML XLink XML验证器 XML DTD XML模式 XML服务器 XML 示例 XML 测试 XML 证书

XML AJAX

AJAX简介 AJAX XMLHttp AJAX请求 AJAX响应 AJAX XML文件 AJAX PHP AJAX ASP AJAX数据库 AJAX应用程序 AJAX 示例

XML DOM

DOM简介归纳 DOM节点 DOM访问 DOM节点信息 DOM节点列表 DOM遍历 DOM导航 DOM获取价值 DOM变更节点 DOM删除节点 DOM替换节点 DOM创建节点 DOM添加节点 DOM克隆节点 DOM 示例

XPath 教程

XPath简介 XPath节点 XPath语法 XPath轴 XPath运算子 XPath 示例

XSLT 教程

XSLT简介 XSL语言 XSLT转换 XSLT <template> XSLT <value-of> XSLT <for-each> XSLT <sort> XSLT <if> XSLT <choose> XSLT申请 客户端上的XSLT 服务器上的XSLT XSLT编辑XML XSLT 示例

XQuery 教程

XQuery简介 XQuery示例 XQuery FLWOR XQuery HTML XQuery条款 XQuery语法 XQuery添加 XQuery选择 XQuery函数

XML DTD

DTD简介 DTD构建基块 DTD元素 DTD属性 DTD元素 vs Attr DTD实体 DTD 示例

XSD Schema

XSD简介 XSD如何 XSD <schema> XSD元素 XSD属性 XSD限制

XSD Complex

XSD元素 XSD Empty XSD元素 Only 仅限XSD文字 XSD混合 XSD指标 XSD <any> XSD <anyAttribute> XSD替代 XSD示例

XSD Data

XSD字串 XSD日期 XSD数值 XSD杂项 XSD 参考

Web Services

XML服务 XML WSDL XML SOAP XML RDF XML RSS

参考

DOM节点类型 DOM节点 DOM节点List DOM NamedNodeMap DOM文档 DOM元素 DOM属性 DOM文字 DOM CDATA DOM评论 DOM XMLHttpRequest DOM解析器 XSLT元素 XSLT / XPath函数

XML Elements


An XML document contains XML元素.


What is an XML Element?

An XML element is everything from (including) the element's start tag to (including) the element's end tag.

<price>29.99</price>

An element can contain:

  • text
  • attributes
  • other elements
  • or a mix of the above
<bookstore>
  <book category="children">
    <title>Harry Potter</title>
    <author>J K. Rowling</author>
    <year>2005</year>
    <price>29.99</price>
  </book>
  <book category="web">
    <title>Learning XML</title>
    <author>Erik T. Ray</author>
    <year>2003</year>
    <price>39.95</price>
  </book>
</bookstore>

In the example above:

<title>, <author>, <year>, and <price> have text content because they contain text (like 29.99).

<bookstore> and <book> have element contents, because they contain elements.

<book> has an attribute (category="children").


Empty XML元素

An element with no content is said to be empty.

In XML, you can indicate an empty element like this:

<element></element>

You can also use a so called self-closing tag:

<element />

The two forms produce identical results in XML software (Readers, Parsers, Browsers).

Empty elements can have attributes.



XML Naming Rules

XML elements must follow these naming rules:

  • Element names are case-sensitive
  • Element names must start with a letter or underscore
  • Element names cannot start with the letters xml (or XML, or Xml, etc)
  • Element names can contain letters, digits, hyphens, underscores, and periods
  • Element names cannot contain spaces

Any name can be used, no words are reserved (except xml).


Best Naming Practices

Create descriptive names, like this: <person>, <firstname>, <lastname>.

Create short and simple names, like this: <book_title> not like this: <the_title_of_the_book>.

Avoid "-". If you name something "first-name", some software may think you want to subtract "name" from "first".

Avoid ".". If you name something "first.name", some software may think that "name" is a property of the object "first".

Avoid ":". Colons are reserved for namespaces (more later).

Non-English letters like éòá are perfectly legal in XML, but watch out for problems if your software doesn't support them.


Naming Styles

There are no naming styles defined for XML elements. But here are some commonly used:

Style Example Description
Lower case <firstname> All letters lower case
Upper case <FIRSTNAME> All letters upper case
Underscore <first_name> Underscore separates words
Pascal case <FirstName> Uppercase first letter in each word
Camel case <firstName> Uppercase first letter in each word except the first

If you choose a naming style, it is good to be consistent!

XML documents often have a corresponding database. A common practice is to use the naming rules of the database for the XML elements.

Camel case is a common naming rule in JavaScripts.


XML元素 are Extensible

XML elements can be extended to carry more information.

Look at the following XML example:

<note>
  <to>Tove</to>
  <from>Jani</from>
  <body>Don't forget me this weekend!</body>
</note>

Let's imagine that we created an application that extracted the <to>, <from>, and <body> elements from the XML document to produce this output:

MESSAGE

To: Tove
From: Jani

Don't forget me this weekend!

Imagine that the author of the XML document added some extra information to it:

<note>
  <date>2008-01-10</date>
  <to>Tove</to>
  <from>Jani</from>
  <heading>Reminder</heading>
  <body>Don't forget me this weekend!</body>
</note>

Should the application break or crash?

No. The application should still be able to find the <to>, <from>, and <body> elements in the XML document and produce the same output.

This is one of the beauties of XML. It can be extended without breaking applications.





W3Schools is optimized for learning and training. 示例 might be simplified to improve reading and learning. Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. While using W3Schools, you agree to have read and accepted our terms of use, cookie and privacy policy.

Copyright 1999-2021 by Refsnes Data. All Rights Reserved.
W3Schools is Powered by W3.CSS.