The goal of preserving the integrity and portability of content and delivering the appropriate level of design to differently enabled browsers and wireless devices is not only the way things should work, but it's also the way they can and do work when designed and built with Web standards.
Web 2.0 Standards
In 1998, Congress amended the Rehabilitation Act to require federal agencies make their information technologies accessible to people with disabilities. Section 508 was enacted to eliminate barriers in information technology, to make available new opportunities for people with disabilities, and to encourage development of technologies that will help achieve these goals. Under Section 508 (29 U.S.C. §794d), agencies must give disabled employees and members of the public access to information that is comparable to the access available to others.
The Web Content Accessibility Guidelines, developed by the Web Accessibility Initiative, are a W3C specification providing guidance on accessibility of Web sites for people with disabilities. These guidelines not only make pages more accessible to people with disabilities, but also have the benefit of making pages more accessible to users using different browsers or one of the emerging handheld or voice-activated computers.
Bear in mind that Web crawlers are, in effect, blind users. The Yahoo, Google and MSN search engines are the three most powerful blind users on the Web, and these users give out recommendations in the form of search results to millions of people every day.
The W3C Document Object Model (DOM) divides Web pages into three separate components: structure, presentation, and behavior.
XHTML, the extensible hypertext markup language, contains text data formatted according to its structural or semantic meaning: headline, secondary headline, paragraph, numbered list, definition list, and so on.
When authored correctly, XHTML markup is completely portable. It works in Web browsers, screen readers, text browsers and wireless devices. Markup can also contain embedded objects along with text equivalents for those who can't view these objects in their browsing environments.
Cascading style sheet (CSS) presentation languages format Web pages, controlling typography, placement, color, and so on. In most cases, CSS can take the place of old-school markup-based layout techniques. In all cases, it replaces nonstandard, outdated junk code that wastes bandwidth and hinders accessibility.
Because presentation is separated from structure, it is possible to change one without negatively affecting the other. For instance, the same layout may be applied to numerous pages or changes can be made to text and links without influencing the layout. The XHTML may be changed at any time without fear because it doesn't serve double duty as a design language. Likewise, the layout can be changed without affecting the markup.