↑
Main Page

DOM Basics

The Document Object Model (DOM) is perhaps the single greatest innovation on the Web since

HTML was first used to connect related documents together over the Internet. The DOM gives

developers unprecedented access to HTML, enabling them to manipulate and view HTML as an

XML document. The DOM represents the evolution of Dynamic HTML, pioneered by Microsoft

and Netscape, into a true cross-platform, language-independent solution.

What Is the DOM?

Before I discuss exactly what the DOM is, you should know what led to its creation. Although the

DOM was heavily influenced by the rise of Dynamic HTML in browsers, the W3C took a step

backward and first applied it to XML.

Introduction to XML

The eXtensible Markup Language (XML) was derived from an earlier language called Standard

Generalized Markup Language (SGML). SGML’s main purpose was to define the syntax of

markup languages to represent data using tags.

Tags consist of text enclosed between a less-than symbol (

) and a greater-than symbol (

), as in

<tag>

Start tags

begin a particular area, such as

<start>

;

end tags

define the end of an area. They

look the same as start tags but have a forward slash (

) immediately following the less-than sym-

bol, as in

</end>

. SGML also defines attributes for tags, which are values assigned inside of the

less-than and greater-than symbols, such as the

src

attribute in

. If

this looks familiar, it should; the most famous implementation of an SGML-based language is the

original HTML.

09_579088 ch06.qxd 3/28/05 11:37 AM Page 159