XML and HTML

HTML, HyperText Markup Language, was derived from SGML, Standard Generalized Markup Language. As HTML and the Web evolved, it became apparent that SGML was not the ideal parent for HTML. A new standard was developed, XML, the eXtensible Markup Language, with a grammar for expressing various document types, of which HTML would be one example. HTML was "adopted" by XML, but taught to observe a stricter more formal code of behavior. In recognition of its good conduct, HTML was granted an "X" to place in front of its name, and was henceforth called XHTML.

HTML or XML pages contain textual descriptions of what is to be presented, in terms of markup language, and the content. The markup language instructs the browser, known as the "user agent" how the content should be presented. Markup consists of an open tag containing the element name and any attributes and their values, and a close tag. Within the scope of a markup can be simple content, or additional marked up content.

Markup can denote paragraphs, font characteristics, tables, refer to images or other multimedia content, or link content to another document. There is no guarantee that a particular markup will be honored, the user agent is free to present the content as it sees fit. It might not have sound, or conversely, it might be a speech device. It could even be sending smoke signals.

More elaborate markup can include scripts which dynamically generate content, or styles that apply rules to classes of content components. In the case of XML, a document type can support whatever markup elements that class of document might need.

A simple example of marked up content:

<p>
This is a paragraph.  I'm a
lasagna hog, go hang a salami.
</p>

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