We have reached a point where many pages on the WWW contain "bad" HTML.
The following HTML code will work fine if you view it in a browser, even if it does not follow the HTML rules:
<html>
<head>
<title>This is bad HTML</title>
<body>
<h1>Bad HTML
</body>
XML is a markup language where everything has to be marked up correctly, which results in "well-formed" documents.
XML was designed to describe data and HTML was designed to display data.
Today's market consists of different browser technologies, some browsers run Internet on computers, and some browsers run Internet on mobile phones and hand helds. The last-mentioned do not have the resources or power to interpret a "bad" markup language.
Therefore - by combining HTML and XML, and their strengths, we got a markup language that is useful now and in the future - XHTML.
XHTML pages can be read by all XML enabled devices AND while waiting for the rest of the world to upgrade to XML supported browsers, XHTML gives you the opportunity to write "well-formed" documents now, that work in all browsers and that are backward browser compatible !!!
XHTML is a family of current and future document types and modules that reproduce, subset, and extend HTML 4 [HTML4]. XHTML family document types are XML based, and ultimately are designed to work in conjunction with XML-based user agents. The details of this family and its evolution are discussed in more detail in [XHTMLMOD].
XHTML 1.0 (this specification) is the first document type in the XHTML family. It is a reformulation of the three HTML 4 document types as applications of XML 1.0 [XML]. It is intended to be used as a language for content that is both XML-conforming and, if some simple guidelines are followed, operates in HTML 4 conforming user agents. Developers who migrate their content to XHTML 1.0 will realize the following benefits:
1- XHTML documents are XML conforming. As such, they are readily viewed, edited, and validated with standard XML tools.
2- XHTML documents can be written to operate as well or better than they did before in existing HTML 4-conforming user agents as well as in new, XHTML 1.0 conforming user agents.
3- XHTML documents can utilize applications (e.g. scripts and applets) that rely upon either the HTML Document Object Model or the XML Document Object Model [DOM].
4- As the XHTML family evolves, documents conforming to XHTML 1.0 will be more likely to interoperate within and among various XHTML environments.
The XHTML family is the next step in the evolution of the Internet. By migrating to XHTML today, content developers can enter the XML world with all of its attendant benefits, while still remaining confident in their content's backward and future compatibility.
