HTML has been in continuous evolution since it was introduced to the Internet in the early 1990's. Some features were introduced in specifications; others were introduced in software releases. In some respects, implementations and author practices have converged with each other and with specifications and standards, but in other ways, they continue to diverge.
HTML 4 became a W3C Recommendation in 1997. While it continues to serve as a rough guide to many of the core features of HTML, it does not provide enough information to build implementations that interoperate with each other and, more importantly, with a critical mass of deployed content. The same goes for XHTML 1, which defines an XML serialization for HTML 4, and DOM Level 2 HTML, which defines JavaScript APIs for both HTML and XHTML. HTML 5 will replace these documents. [DOM2HTML] [HTML4] [XHTML1]
The HTML 5 draft reflects an effort, started in 2004, to study contemporary HTML implementations and deployed content. The draft:
1. Defines a single language called HTML 5 which can be written in HTML syntax and in XML syntax.
2. Defines detailed processing models to foster interoperable implementations.
3. Improves markup for documents.
4. Introduces markup and APIs for emerging idioms, such as Web applications.
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