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People like things to be as simple as possible, while still leaving some differentiation and choice: two major political parties; two teams in a football match; two browsers. But the two major browsers run on several different platforms in several different versions, and the fact that a page looks OK in the most popular versions of the major browsers on your PC or Mac is no guarantee that it looks the same on all others. Furthermore there are several other browsers accounting for several percent of the total share.

The Internet and the World Wide Web was originally the province of technical types who were comfortable and familiar with notions of 'correctness' in computer languages. The popularisation of the WWW has led to the influx of many new users of the technologies who don't know about or want to get involved in the tedious meticulousness of formal computer languages, and the fact that browsers are very forgiving about not-quite correct HTML allows them to focus on the content - which is a Good Thing - but which may result in that content not being accessible to everyone. For them (and for the techies) there are "HTML checkers" that are relatively easy to use and understand. First, let's clarify the terminolgy..

HTML Validation has historically referred to the process of checking that some HTML code conforms to a very precisely formulated definition; we'll discuss this in more depth later in this article. However, the term has become diluted with popular usage, and some people now use 'validation' to mean the stylistic analysis of code to recommend improvements, such as reducing image sizes, adding dimensional attributes on IMG tags, closing table (row and cell) tags, etc. Other people (myself included) would prefer that this process would be called HTML checking, because the term 'validation' has a more precise meaning which continues to be useful, as we'll see later.

HTML standards compliance in a web page can be checked by using a 'validator'. These are programs that check the structure of a web page rather precisely, and tend to not be especially easy to use. Before getting immersed in one of these, it's perhaps easier to start with the more user-friendly 'HTML checkers'. The typical use of a strict 'validator' is to check code for conformance to a specific representation of some version of HTML - usually but not always, a W3C standard. But since the browser makers rarely if ever supply a formal representation of their HTML support (known as a 'DTD') strict validators can't check for correct Netscape/Microsoft code unless a DTD is reverse-engineered.

Errors in web pages typically fall into three classes:-

1. Use of proprietary extensions - other browsers are unlikely to understand these (e.g. BLINK or MARQUEE) so you have to judge whether their use is appropriate.

2. Omission - something was left out that should not have been, e.g. ALT attributes in IMG tags; double quotes around attribute values; etc. These are almost always trivial to fix.

3. Bad syntax - like jumbling up the words in an English sentence, the tags aren't placed correctly relative to each other, or aren't correctly ended. An example is putting multiple blocks inside character formatting, such as <p> inside <b> ... </b> This type of error can be more difficult to understand and to fix, but it gets easier with practice.

Some useful HTML checkers are:-

• Web Site Garage, which I've successfully used to "tune up" the WDVL home page.

• SiteInspector checks your site's HTML design, load time, dead links, spelling, site popularity and search engine readiness.

• NetMechanic offers an HTML checker, but I'm not sure that it really checks what it claims - e.g. when I ran it against a page known to be technically valid HTML 4.0, using its HTML 4.0 option, it claimed there were errors.

• Doctor HTML is a Web page analysis tool which retrieves an HTML page and reports on any problems that it finds. The primary focus of this tool is to provide a clear, easy-to-use report of information that is relevant for improving your Web page.

• Weblint - "a syntax and minimal style checker for HTML: a Perl script which picks fluff off html pages, much in the same way traditional lint picks fluff off C programs." ('lint' is the name of a well-known UNIX program which offers suggestions for improving C programs).

Parlez Vous HTML ?