The main building blocks of both XML and HTML documents are elements.

The Building Blocks of XML Documents

Seen from a DTD point of view（从dtd的角度来看）, all XML documents (and HTML documents) are made up by the following building blocks:

  • Elements
  • Attributes
  • Entities
  • PCDATA
  • CDATA

Elements

Elements are the main building blocks of both XML and HTML documents.

Examples of HTML elements are "body" and "table". Examples of XML elements could be "note" and "message". Elements can contain text, other elements, or be empty. Examples of empty HTML elements are "hr", "br" and "img".

Examples:

<body>some text</body>

<message>some text</message>

Attributes

Attributes provide extra information about elements.

Attributes are always placed inside the opening tag of an element. Attributes always come in name/value pairs. The following "img" element has additional information about a source file:

<img src="computer.gif" />

The name of the element is "img". The name of the attribute is "src". The value of the attribute is "computer.gif". Since the element itself is empty it is closed by a " /".

Entities

Some characters have a special meaning in XML, like the less than sign (<) that defines the start of an XML tag.

Most of you know the HTML entity: "&nbsp;". This "no-breaking-space" entity is used in HTML to insert an extra space in a document. Entities are expanded when a document is parsed by an XML parser.

The following entities are predefined in XML:

Entity References Character
&lt; <
&gt; >
&amp; &
&quot; "
&apos; '

PCDATA

PCDATA means parsed character data.

Think of character data as the text found between the start tag and the end tag of an XML element.

PCDATA is text that WILL be parsed by a parser. The text will be examined by the parser for entities and markup.

Tags inside the text will be treated as markup and entities will be expanded.

However, parsed character data should not contain any &, <, or > characters; these need to be represented by the &amp; &lt; and &gt; entities, respectively.

CDATA

CDATA means character data.

CDATA is text that will NOT be parsed by a parser. Tags inside the text will NOT be treated as markup and entities will not be expanded.

DTD - XML Building Blocks的更多相关文章

  1. Intel® Threading Building Blocks (Intel® TBB) Developer Guide 中文 Parallelizing Data Flow and Dependence Graphs并行化data flow和依赖图

    https://www.threadingbuildingblocks.org/docs/help/index.htm Parallelizing Data Flow and Dependency G ...

  2. bc.34.B.Building Blocks(贪心）

    Building Blocks Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/65536 K (Java/Others) ...

  3. 企业架构研究总结（35）——TOGAF架构内容框架之构建块（Building Blocks）

    之前忙于搬家移居,无暇顾及博客,今天终于得闲继续我的“政治课”了,希望之后至少能够补完TOGAF方面的内容.从前面文章可以看出,笔者并无太多能力和机会对TOGAF进行理论和实际的联系,仅可对标准的文本 ...

  4. TOGAF架构内容框架之构建块（Building Blocks）

    TOGAF架构内容框架之构建块(Building Blocks) 之前忙于搬家移居,无暇顾及博客,今天终于得闲继续我的“政治课”了,希望之后至少能够补完TOGAF方面的内容.从前面文章可以看出,笔者并 ...

  5. XML概念定义以及如何定义xml文件编写约束条件java解析xml DTD XML Schema JAXP java xml解析 dom4j 解析 xpath dom sax

    本文主要涉及:xml概念描述,xml的约束文件,dtd,xsd文件的定义使用,如何在xml中引用xsd文件,如何使用java解析xml,解析xml方式dom sax,dom4j解析xml文件 XML来 ...

  6. HDU—— 5159 Building Blocks

    Problem Description After enjoying the movie,LeLe went home alone. LeLe decided to build blocks. LeL ...

  7. DTD -- XML验证

    DTD(文档类型定义)的作用是定义 XML 文档的合法构建模块. DTD 可被成行地声明于 XML 文档中,也可作为一个外部引用. DTD简介 内部的 DOCTYPE 声明 假如 DTD 被包含在您的 ...

  8. [翻译]Review——How JavaScript works：The building blocks of Web Workers

    原文地址:https://blog.sessionstack.com/how-javascript-works-the-building-blocks-of-web-workers-5-cases-w ...

  9. 四、Implementation: The Building Blocks 实现：构件

    四.Implementation: The Building Blocks 实现:构件 This is the essential part of this guide. We will introd ...

随机推荐

  1. poj 2454 Jersey Politics 随机化

    随机化算法+贪心! 将3*k排序后分成3分,将第二第三份的和分别加起来,让和与500*k比较,都大于则输出,否则,随机生成2个数,在第二第三份中交换! 代码如下: #include<iostre ...

  2. WebLoigc的配置（生产模式与开发模式）

    1.Weblogic两种模式的切换1).生产模式--->开发模式将domain路径下的bin\setDomainEnv.cmd文件中set PRODUCTION_MODE=true改为set P ...

  3. mac 用 brew

    mac 下用   brew 安装插件, 有重复的不会再次安装,比xmap模式好

  4. 【原创】海量数据处理问题（一） ---- 外排，堆排，K查找的应用

    这篇博客源自对一个内存无法处理的词频统计问题的思考,最后给出的解决办法是自己想的,可以肯定这不是最好的解法.但是通过和同学的讨论,仍然感觉这是一个有意义及有意思的问题,所以和大家分享与探讨. 如果有误 ...

  5. jquery uploadify上传文件插件导致浏览器崩溃问题解决方法

    自谷歌浏览器更新到(版本39.0.2171.99 )后,访问上传文件界面浏览器就崩溃了,而其他的浏览器不会出现问题. 出现这种问题的原因就是谷歌浏览器缓存问题,但将访问该jsp页面路径添加上时间戳后无 ...

  6. 【HDOJ】4393 Throw nails

    水题,优先级队列. /* 4393 */ #include <iostream> #include <sstream> #include <string> #inc ...

  7. Shell中判断字符串是否为数字的6种方法分享

    #!/bin/bash ## 方法1 a=1234;echo "$a"|[ -n "`sed -n '/^[0-9][0-9]*$/p'`" ] &&a ...

  8. js压缩、混淆和加密

    最近看到有些论坛在讨论js压缩.混淆和加密的问题,特意找了些资料看了下,现在总结一下: 1.关于三者的定义与区别 压缩:删除 Javascript 代码中所有注释.跳格符号.换行符号及无用的空格,从而 ...

  9. Visual Studio Developer Command Prompt删除localdb的方法

    PM> sqllocaldb.exe stop v11. LocalDB instance "v11.0" stopped. PM> sqllocaldb.exe de ...

  10. FormsAuthentication实现单点登录

    原文地址:http://www.wlm.so/Article/Detail/lmb48bk9f690n00000 单点登录,这种在网络非常常见,在这里讨论的是实现同一主域下的子站间的单点登录,同样也适 ...