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Introduction

Introduction

HTML has opened up the world of publishing on the World Wide Web to anyone who cares to learn its tags and attributes, but it provides limited facility for the kind of layout control that some users (desktop publishers, for instance) are used to having. That's because the initial design philosophy behind HTML largely focuses on designating the structural elements of a document, while leaving the individual layout decisions up to the Web browser to figure out. As HTML and Web browser technology have progressed over time, however, a certain amount of control over the appearance of a Web page has been added into HTML, primarily in an ad hoc fashion in the form of extensions to HTML developed by Netscape and Microsoft. These extensions to HTML, however, run contrary to the original philosophy behind HTML (which is to specify the structure, and not the appearance, of a document), while still falling far short of the kind of precise control desktop publishers are used to having.

Part of the reason for this focus on structure versus appearance goes back to the bandwidth-starved early days of Web publishing, when most people were still connecting at 14 kbps or less and the Internet backbone had considerably less capacity than it has today. The thinking was that allowing Web publishers to individually design their own Web pages, rather than rely on browsers to largely do it for them, would lead to over-consumption of a scarce resource, bandwidth, that we all have to share. This is not a concern that desktop publishers have, in that their DTP documents only need to consume resources available on their local machines.

Although bandwidth is much more plentiful than it was in the early days, bandwidth-availability is still a concern on the Web and the Internet. Even broadband connections using DSL and cable modems are often slowed to a crawl due to traffic jams on the information superhighway.

The solution to the problem of providing more formatting control while continuing to conserve bandwidth is one that desktop publishers are already very familiar with: style sheets. The initial standard for using style sheets on the Web, Cascading Style Sheets, level 1 (CSS1), was recommended as early as December of 1996, although it is only now being fully supported by current Web browsers. A second level, Cascading Style Sheets, level 2 (CSS2), was recommended in May of 1998, but it is only partially supported by current Web browsers.

Another reason behind separating appearance from content is accessibility. If HTML is handling both the structure and the appearance of a document, a non-graphical or non-visual browser, such as a text browser, speech browser, or Braille browser, might have difficulty separating structure from appearance, making access to the document for visually impaired individuals more difficult. However, if HTML is used only to control the structural elements of a page, while style sheets are used to control its appearance, then a non-visual browser, for instance, can easily ignore the document's appearance and focus in on its structural content. Style sheets can also be used to add in presentation features that are specifically aimed at non-visual browsers, for instance, such as specifying pauses prior to, or pitch or tonal changes for, major headings within a document.

Cascading Style Sheets (CSS) also helps to enable the creation of fluid Web page designs that can be scaled in relation to a user's default settings. For instance, a user may reset his browser's default settings to display a larger default font size, due to a visual impairment that makes reading the usual default font size difficult or impossible. Using CSS, Web authors and designers can create Web page designs and layouts that use relative font sizes and other measurements that will be based on a user's default preferences. CSS also allows users to specify their own style sheet, thus participating in the determination of how Web pages will be displayed on their local computer.

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