The Many Flavours Of HTML.

HTML (Hypertext Markup Language) is the language of the web – every website out there is written in some kind of HTML. Because of the rapid evolution of the web, though, HTML grew quickly in a very unplanned way, which can lead to problems if you're not sure what kind or version of HTML you're using. Here's a quick history of HTML's flavours so far.

A Long, Long Time Ago...

The first version of HTML was created by the web's inventor, Tim Berners-Lee, and was loosely based on an existing standard called SGML (Standardised General Markup Language). This very first version didn't have an img tag, which meant that no graphics at all could appear on web pages. Berners-Lee informally extended the language, but didn't standardise it.

As the web grew, the lack of standardisation started to make it difficult for web browsers to interact – one web browser might have a new tag that others didn't support, meaning that people would see pages completely differently depending on which browser they used. In 1995, HTML was formalised as a standard named HTML 2, which was the version that the first mass-market web browsers were based on.

As they extended the standard further, an HTML 3 was introduced in 1997 to keep up-to-date. HTML 4 was introduced later that year as an effort to clean up the standard, making it clear that some tags should no longer be used. Apart from a few minor fixes in 1999, this is the version of HTML that is still in use today.

DHTML.

Parallel to this development, though, other languages were being developed that could be included in HTML documents: languages like Javascript (for interactive pages) and CSS (for styling). DHTML (Dynamic HTML) was the name given to the combination of HTML and these technologies. To put it simply, HTML is for web pages while DHTML is for 'web applications'. As people start to do more and more things on the web that they used to do with separate programs, DHTML techniques are becoming ever-more popular.

XHTML.

Sometimes considered 'next-generation HTML', XHTML is a stricter version of HTML that makes it follow XML standards. XML (eXtensible Markup Language) is a standard for HTML-like languages that is being used for more and more purposes, including configuration and sharing data.

Stripped of the technical talk, XHTML can basically be thought of as a stricter version of HTML. Where HTML is often messy and hard to test, XHTML is strictly standardised and can be run through automatic 'validators' that will point out any errors you've made. This improves cross-browser compatibility and makes web pages much easier to maintain, since it mostly forces information on the style of the page to be separated from the actual text of the page.

XHTML exists in a few different versions: there is a 'transitional' version, which lets you keep using some old practices from HTML4, and there is a 'strict' version, which is the one you need to use to get most of XHTML's benefits.

The web's standards body, the W3C, runs an HTML validator at validator.w3c.org.

What Does All This Mean to Me?

You might be wondering at this point why exactly you need to know about the different kinds of HTML. Well, as ever, the answer is that you need to choose one before you start developing your website. You have to be aware of which versions your tools support to know whether your tools can work together, and you should aim to pick the kind of HTML that will be most suitable for your site.

At the moment, XHTML is recommended for most websites, simply because it makes the whole process much easier, especially if you use an editor that saves to XHTML automatically. The only situation in which you should really keep using HTML4/DHTML is if you're designing a web application instead of a web page. If your site is, like 99% of the sites on the web, designed to give information more than it is designed to do anything else, then you should be using XHTML, preferably the strict version.