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Intro to Markup Languages
Last updated Oct 17, 2003.
By Molly Holzschlag
One way to ease the challenge of navigating current and emerging markup languages is to first understand what markup really is and then to understand the markup timeline and how we got to the languages we're using for the Web today.
So what is markup, really? Remember when you got a test or essay back in school, and the teacher marked it up with a red pen? The teacher's comments and suggestions are the essence of markupthe information is tagged in some way to have you modify it in some wayadd punctuation, break long passages of text into paragraphs, and so on. Markup languages do the same thing: tag information and define that information, for example, using paragraph tags to define a paragraph of text.
In order to manage technical documents within large organizations (such as IBM), a specification called the Standardized General Markup Language (SGML) was created. SGML is a very complicated specification, and is referred to as a "meta" language. This means it's not a language per se, but its rules of structure and syntax are used to make other languages and applications for marking up those technical documents.
When Tim Berners-Lee created the infrastructure that became the World Wide Web, he looked to SGML as a means to create a streamlined markup language that would help authors of Web documents mark up those documents in definable order and structure. When HTML first came to be, it was a very simplistic language, with tags that focused only on defining paragraphs, breaks, and lists. Remember, HTML was created before the Web was visual, so it was not meant to be a language of presentation, just a way to organize text information for display onscreen.
Of course, the first visual browser, Mosaic, changed all that. And the subsequent "Browser Wars"the period of time in which Netscape and Microsoft battled it out for featuresexpanded the original, simple, and easily standardized HTML into a complicated mess.
CSS and XML Emerge
During this time, two other technologies were emerging that would force a powerful re-evaluation of markup. One of those technologies is EXtensible Markup Language (XML). Also created from SGML, XML can be considered "SGML Lite." Like SGML but unlike HTML, XML is a meta-language. It's used to create other languages and custom applications, and it was streamlined specifically for use on the Web. The other important technology insofar as Web designers are concerned is Cascading Style Sheets (CSS), a language that can be used to manage the presentational aspects of a Web page.
With CSS on the scene, the W3C began to address presentational concerns within HTML; as a result, the HTML 4.0 specification offered a variety of means for Web designers to transition to stricter, more standardized practices. A critical message within HTML 4.0 was to encourage the separation of presentation and structure, moving Web designers away from relying on tables and proprietary techniques to achieve their design goals.
HTML 4.01 is a minor editorial upgrade to HTML 4.0, but it's of historical importance because it is the last version of HTML. With XML on the scene, HTML was reformulated as an XML rather than SGML application, and this resulted in XHTML 1.0. XHTML 1.0 follows the vocabulary of HTML 4.01, but adheres to the much stricter syntax available within XML.
More About XHTML
Is XHTML different from HTML as a result? In some ways, yes. The way that elements, case, quotes, and other aspects of the syntax are handled are more strict and detailed.
Be sure to check the references later in this section to learn more about the differences between XHTML and HTML.
For purposes of this discussion, the function of these two languages for Web designers is essentially the same, and which language you choose is less important than how well you conform to the ideals of the language.
Although XML has been used in numerous ways (most of them behind-the-scenes management of data), its influence has changed the future of markup and how it will be used. The same is true of CSS. Both the influence of XML and the emergence of browsers with good support for CSS are changing the way Web designers are working.