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In an interview I was asked a question that I'd never thought about, which was "We already have HTML which fulfills all the requirements of writing a web page, so what's the need for XHTML?"
I Googled a lot and also read many articles, but I'm not able to get properly why XHTML has been introduced. Please explain to me.
XHTML is an attempt to encourage the development of "well-formed" HTML.
HTML has evolved over more than 10 years. Its implementation, and the implementation of the browsers that parse and render it, are not exactly consistent. This is why cross-browser compatibility is a major headache.
HTML is based on SGML (Standard Generalized Markup Language.) XML is also derived from SGML, so they are cousins of a sort. XHTML marries the two, providing (in theory) the benefits of XML to HTML. This includes a well-defined schema that can be reliably validated, queried, and transformed.
Because it is valid XML. That helps a lot since you can use a lot of tools originally designed for XML, such as XML parsers, XSLT, XPath, XQuery, ...
Normal HTML is a SGML dialect and that is not parsable without knowledge of the schema.
is correct HTML but not correct XML. If you want to parse that, you have to know that
ul-elements have to be closed butlis don't.XHTML also allows you to embed other XML dialects like MathML, Ruby, SVG, etc. (You can also embed XHTML in other XML dialects, if desired.)
If you are just 'making a web page', you don't necessarily need XHTML. But if you are programmatically generating a page, you might find that the tools for generating XML are better than those that generate HTML.
In a nutshell: XHTML is often only beneficial and preferred over HTML whenever you want to use a XML based tool to manipulate/transform/generate HTML pages on the server side.
Lot of examples can be found in component based MVC frameworks like
SunOracle JSF which uses Facelets as a XHTML based view technology. The server side components are definied in XSD's and the pages are parsed using a SAX parser. You can even add a<!DOCTYPE html>to top of the page to let Facelets generate "pure" valid and strict HTML5. Microsoft ASP.NET MVC has a similar view technology.When you're hand-writing HTML, XHTML doesn't add much benefit, or it must be pushing off the "coolness" of using a (over)hyped technology.
See also: