XHTML
January 26th 2000: The World Wide Web Consortium (W3C) releases the first specification of the markup language that is intended to substitute HTML. That language is called XHTML and its specification it’s in one page only. There are no new tags; there is no revolutionary difference since HTML 4.0. However, what is now the W3C’s recommended language is definitely a fundamental step in the developing of web pages.

The key element is the ‘X’, which stands for EXTENSIBLE, is the same X on which is based the digital communication’s cornerstone of the future: XML (Extensible Markup Language). This is the real revolution: HTML is now part of the XML family, it shares the rules and the potentiality with the result of no more “messed but it works” code.

To define what XHTML is we can begin with a simple expression:

HTML + XML = XHTML

HTML
Hyper Text Markup Language, it’s a language used by browsers to visualize the content of a web page. Its simplicity is the base of the Internet boom.

XML
It’s a sort of “super-language” that allows the development of new markup languages. Powerful, flexible and efficient, it’s the base of all the new technologic specifications released by W3C and adopted now as the standard for the IT industry. The main aims of XML, declared in the first official specification (October 1998), are few and explicit: employ of the language on the Internet, easiness of the documents creation, support of many applications, clarity and comprehensibility.

XHTML
XHTML is the HTML reformulation as XML application. This basically means one thing: A XHTML document must be valid and well formed.
Rather then develop a new version of the language, a HTML 5.0, the consortium staff has simply done a redefinition work. No new tags, attributes or methods. These are exactly the same as in HTML 4.0. Basically the dictionary is still the same but the syntax changes. Considering this fact, it’s clear how XHTML respond to two important requirements:

- To take HTML into the XML family with the benefits that this bring in terms of extensibility and strict syntax.

- To maintain the compatibility with all the software that supports HTML 4.0.

Thought in this way, XHTML is a bridge between the past and the future. It’s a way to learn to think in XML starting from a language that we know, without renouncing the already acquired knowledge.

XHTML versions
Three are so far the versions of XHTML published by W3C.

XHTML 1.0
Published on January 26th 2000 and followed by a revisited version of October 2001. It consists on the re-writing of HTML 4.0 in XML and it is based on the three DTD already defined for this language:

DTD Strict
DTD Transitional
DTD Frameset

XHTML Basic
It is a basic version of the language. Specifically thought for mobile devices (PDA, Mobile phones), it contains only the elements that can be adapted to these devices (it excludes, for example, the frames that are never going to be used for that context). It is destined to substitute WML as the base language for WAP applications.

XHTML 1.1
Based on the 1.0 version’s DTD Strict, it represents the first practical formulation of the modularization concept. In this view, the fundamental elements (basically the whole the tags that define the document structure) are grouped in a variety of independent modules, which can be implemented or excluded according to the necessity. W3C reckons it’s the base of the future extension of XHTML with others languages sets or modules.