This article constitutes section 1, part B, chapter 9 of the CIW Website design manager course and briefly covers: HTML Extensions.

Extending HTML

The rise in user abilities and expectations has resulted in the continual improvements and extension of HTML, which included Cascading Style Sheets (CSS), JavaScript, Dynamic HTML (DHTML) and Extensible Hypertext Markup Language (XHTML).

Cascading Style Sheets (CSS)

This is a specification for creating lists of formatting instructions, called style sheets, which can be used to customise Web pages. You can create style sheets in the HTML document (inline style), or create an external style sheet to which one or more documents may refer.

CSS are not really HTML extensions, rather an additional specification.

The HTML flavour HTML 4.01 Strict demands that you use only CSS to impose layout and formatting for your pages.

The concept of inheritance is essential to Cascading Style Sheets. In fact the word “Cascading” refers to inheritance. The style you define will flow, or cascade, throughout the document, unless another style specifically overrides it.

CSS, DHTML and XML are all HTML extensions that extend the scope of the Web Site designerJavaScript for HTML Extensions

Javascript is just one of the possible HTML Extensions that are available to the Web site designer. JavaScript is an object-based scripting language that allows developers to add interactivity to their Web pages. The CIW course tells us that JavaScript must be contained within the HTML document, I beg to differ, it can be in an external file referenced from the HTML document. Certain functionality can, probably, only be achieved with embedded script. An external file will, however, appear to the browser as if it were embedded as the external file is loaded with the page.

Document Object Model (DOM)

A Document Object Model (DOM) describes the elements, or objects, within a document rendered by a Web browser. It is intended to be a vendor-neutral, cross-platform standard. With the DOM, you can open a new browser instance and control its functions.

The DOM is not as universal as was expected. Each of the major browsers uses its own DOM. The W3C DOM specification can be found at:

Dynamic HTML (DHTML)

Dynamic HTML (DHTML) is an HTML enhancement that allows animation, interaction, and dynamic updating in Web pages. With DHTML, you can create a Web pao-e that reacts to user actions without contacting the server or downloading complex, bandwidth-consuming applications. Because it eases the burden on the server, DHTML is an effective front-end and back-end solution. You can use DHTML to control the way in which an image will perform. For example, ou can make an image become animated only when a mouse passes over it. Or the page can automatically scroll text headlines, similar to a Java applet or ActiveX control.

Additional DHTML uses include the following:

  • Automatic adjustment of font sizes and colors. You can use a DHTML event handler to animate text when a user passes a mouse over certain parts of the page.
  • Absolute positioning. You can create text that moves to certain positions in reaction to user input.
  • New document content without having to refresh the browser window.
  • Granular control over animation, audio, and video. Rather than coding a page to constantly present a video clip, you can code it to begin a sequence at a certain time. or after a certain event.

Improve the look and feel of your new web pageExtensible HTML (XHTML)

XHTML is considered one of the HTML Extensions combining HTML and XML. In January 2000, HTML and Extensible Markup Language (XML) were combined into a specification called Extensible HTML (XHTML). XHTML relies on the HTML 4.01 and the XML 1.0 specifications. Because of this reliance, the XHTML specification is relatively condensed. You can read the XHTML specification at

The W3C specification defines XHTML as “a reformulation of HTML 4 as an XML 1.0 application, and three DTDs corresponding to the ones defined by HTML 4.” Whereas HTML describes a document’s visual layout, XML allows you to describe the function and context of the actual information contained in a document. XML is a tool that will help describe and organize the data that passes through networks. In Web-based computing, you must understand when to use a particular tool. XML enables developers to create persistent documents that can be searched quickly and efficiently.

Extensible Markup Language (XML)

XML is pehaps the most powerful of the HTML Extensions. XML is a language that allows you, within certain limits, to create your own custom markup language. Technically, you do not use XML to describe the meaning of information in your document. You use it to create your own language that in turn describes the meaning of information in your document. In this sense, XML is a meta-language: a language used to create languages. Any tags you define yourself are said to extend XML.

The chief benefit of XML is that it enables you to focus on the meaning and context of the information in a document. Banks, e-commerce sites, search engines and large networks that serve complex documents require just such a solution.

XML is, in many ways, a reduced version of Standard Generalised Markup Language (SGML), because it allows you to declare your own tags without the complexity of SGML. The W3C now governs the development of XML.

This post about HTML extensions has been unashamedly purloined from the extensive notes provided with the CIW Course.

I find it has a poor Flesch Reading Ease score in my Yoast SEO plugin tool. But, that is hardly surprising given that these notes are of a technical nature.

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