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Professional CSS: Cascading Style Sheets for Web Design, Second Edition by Mark Trammell, Dunstan Orchard, Ethan Marcotte, Cindy Li, Todd Dominey, Christopher Schmitt

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Appendix B. Rules for HTML-to-XHTML Conversion

Hypertext Markup Language (HTML) is a simple language that led to the boom of the Web in the 1990s. However, its simplicity was also a roadblock to progress. The early success of HTML attracted a larger Web developer audience and spawned a desire to push the medium. HTML outgrew its simple upbringing.

For example, while placing images in a Web page is easy to do with HTML, placing the images in a specific location on a Web page is impossible without violating the intent of the table tag. Another example is placing the multimedia content in a Web page, which usually results in the use of invalid, proprietary elements and attributes.

In addition, HTML contains a limited set of elements and attributes. Other industries such as engineering or chemical companies couldn't mark up their formulas. Instead of writing an all-encompassing version of HTML, the W3C worked on Extensible Markup Language (XML), which is a flexible meta-language.

XML provides the framework for other markup languages to be created. Other industries can create their own markup languages rather than face a restrictive environment such as HTML.

However, for most Web developers who are familiar primarily with HTML, the major benefits of XML (creating new elements and specifying their treatment) are not important. Instead, the elements found in HTML will be of the most use.

The W3C reformulated HTML from the XML standard to create backward compatibility while making the language ...

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