Platinum Edition Using HTML 4, XML, and Java 1.2
(Publisher: Macmillan Computer Publishing)
Author(s): Eric Ladd
ISBN: 078971759x
Publication Date: 11/01/98

Part V
Java Script

CHAPTER 24
Introduction to Dynamic HTML

by Jim O'Donnell

In this chapter

What Is Dynamic HTML? 582

Web Page Layout and Content Positioning 585

Dynamic Styles with Cascading Style Sheets 592

Web Browser Object Model 596

Dynamic Fonts 598

What Is Dynamic HTML?

When HTML was first developed, its mixing of text and graphics, as well as the inclusion of the hypertext link for linking information, revolutionized the way information was presented and distributed across the Internet. Since the inception of HTML, Web developers and vendors have been looking for ways to present information more dynamically and to create more ways to interact with the user. Animated GIFs, Web browser plug-ins and ActiveX Controls, Java applets, and scripting languages are all examples of ways to make Web pages more exciting.

HTML itself is basically a static language, however; information is sent to a client Web browser, which renders it for the viewer. To add movement or animation to an HTML document, it was necessary to embed some other element, such as the Java applets or ActiveX Controls mentioned in the preceding paragraph. Macromedia’s Shockwave, for example, has long been used to add increased animation and interactivity to many Web pages.

With version 4 of their latest Web browser applications, however, both Netscape and Microsoft have introduced a new technology, dubbed “Dynamic HTML,” which seeks to make HTML more interactive in its own right. Through each company’s version of Dynamic HTML, Web developers have increased control over the appearance of an HTML document as rendered on a compatible Web browser and have more ways to make the document dynamic and interactive, capable of better detection and response to user actions.

What exactly is Dynamic HTML? Unlike the current state of such languages and technologies as HTML, Java, and VRML, Dynamic HTML is not a standard; it is not enacted, proposed, or even being developed by any Internet standards organization. Rather, Dynamic HTML is a term applied by both Netscape and Microsoft to a collection of technologies that they are developing for making HTML documents more dynamic and interactive. Although a few common elements exist, the question “What is Dynamic HTML?” has a different answer, depending on whom you ask.

The remainder of this chapter will give you an introduction to the different capabilities in Netscape Navigator and Microsoft Internet Explorer under the guise of “Dynamic HTML.” The next two chapters will take a more in-depth look, first at Netscape and then at Microsoft Dynamic HTML. Finally, you will finish this section by learning how to use Dynamic HTML to develop your Web pages in such a way that they are compatible with both browsers.

Netscape’s Answer

Netscape’s documentation for its version of Dynamic HTML, along with a lot of other documentation, demos, and other good information about Netscape software and technologies, is located on its DevEdge Online Web site, which can be found at

http://developer.netscape.com/

The specific URL for its Dynamic HTML documentation can be found at

http://developer.netscape.com/tech/dynhtml/index.html

According to this information, Netscape’s answer to the question “What is Dynamic HTML?” would consist of the following elements, which were first introduced into Netscape Navigator version 4:

•  Style sheets— Microsoft first implemented support for Cascading Style Sheets (CSS), MicrosoftCSS, in its Internet Explorer version 3.0, and Netscape added it to its Web browser with version 4 and above. Both Netscape and Microsoft support the Cascading Style Sheets standard adopted by the World Wide Web Consortium (W3C). You can find these standards on W3C’s CSS Web site.
See “What Are Style Sheets?,” p. 262.

Netscape considers style sheets a part of its implementation of Dynamic HTML because it has extended its Web Browser Object Model to include style sheets and styles attached to tags within an HTML document. This enables the formatting information for the content within the HTML document to be changed dynamically using JavaScript.

	ON THE WEB
	http://www.w3.org/Style/ This Web site houses the W3C’s complete Cascading Style Sheet definition, as well as a number of links you can follow to find out more.

•  Content positioning—With the early beta releases of Netscape Navigator version 4, Netscape introduced the <LAYER> and <ILAYER> tags, which were their proposed HTML tags to allow for precise 2D and 3D positioning of elements within an HTML document. These tags were rejected by the W3C, although Netscape still supports them in the release version of its Web browser.
With the rejection of the <LAYER> and <ILAYER> tags, Netscape added support for what is known as CSS positioning. In addition to the formatting options that can be specified using style sheets, Netscape also includes support for positioning the elements to which they are attached. Whether you create your HTML elements to be positioned using the <LAYER> or <ILAYER> tags, or whether you use CSS positioning, Netscape enables you to use JavaScript to reference those elements the same way, enabling you to dynamically change their positions.

•  Downloadable fonts—One problem with using style sheets to achieve your desired formatting effects is that they work only if your users have the same fonts installed on their local systems. If they do not, your carefully constructed Web page will be rendered using a font different from the one you intended, potentially destroying the desired effect.
Netscape has developed a solution to this problem, which it groups as a part of its Dynamic HTML. It has added a way for you to set up and embed fonts in your HTML documents, which are then downloaded over the Web along with the document so that you can be sure it will be correctly rendered.