DTD Building Blocks

|  | Search W3Schools : |

HOME | HTML | CSS | XML | JAVASCRIPT | ASP | PHP | SQL | MORE... |  | References | Examples | Forum | About

ADVERTISEMENTS XML Certification Download XML editor Custom Programming |  |

Table of contents

DTD Tutorial
DTD HOME
DTD Introduction
DTD Building Blocks
DTD Elements
DTD Attributes
DTD Elements vs Attr
DTD Entities
DTD Validation
DTD Examples
DTD Summary

Selected Reading

Web Statistics
Web Glossary
Web Hosting
Web Quality
W3Schools Tutorials
W3Schools Forum
Helping W3Schools

# DTD - XML Building Blocks

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, 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.

## Learn XML with <oXygen/> XML Editor - Free Trial!

oXygen helps you learn to define, edit, validate and transform XML documents. Supported technologies include XML Schema, DTD, Relax NG, XSLT, XPath, XQuery, CSS.

Understand in no time how XSLT and XQuery work by using the intuitive oXygen debugger!

Do you have any XML related questions? Get free answers from the oXygen XML forum and from the video demonstrations.

Download a FREE 30-day trial today!

WEB HOSTING
Ecommerce Components for ASP.NET
$15 Domain Name Registration Save $20 / year!
Buy UK Domain Names Register Domain Names
Cheap Domain Names Cheap Web Hosting
Best Web Hosting
PHP MySQL Hosting
Top 10 Web Hosting
UK Reseller Hosting
Web Hosting
FREE Web Hosting

WEB BUILDING
Website Templates Flash Templates Website Builder Internet Business Opportunity
Custom Programming
FREE Trial or Demo Web Content Manager Forms,Web Alerts,RSS
Download XML editor
FREE Flash Website
FREE Web Templates

EDUCATION
US Web Design Schools
HTML Certification
JavaScript Certification
XML Certification
PHP Certification
ASP Certification

HOME or Top of Page |  | Printer Friendly
W3Schools is for training only. We do not warrant the correctness of its content. The risk from using it lies entirely with the user. While using this site, you agree to have read and accepted our terms of use and privacy policy. Copyright 1999-2009 by Refsnes Data. All Rights Reserved.