A large number of Web browsers are based on NSCA Mosaic, the original graphical Web browser available free on the Internet. The leading alternative is Netscape Navigator. Internet access providers frequently supply proprietary browsers with their service. The leading non-graphical Web browser is Lynx which is available for Mac, DOS and Unix platforms. The flexibility and richness of the Web also presents the greatest access challenges.
Web documents contain some information in exclusively audio, visual and graphic form.
Frequently, critical components of a document have graphics only labels. Hypertext links can occur anywhere in a document and are identified by purely graphical characteristics such as color, bolding or graphic images with colored outlines. With the exception of Lynx and other text based browsers, most Web browsers have graphical user interfaces. Web documents are created with the assumption that the browser will display graphics, video and audio. Document Structure and Content A number of these problems can be resolved by carefully designing the HTML documents.