What they are and why they are important.
In the bad old days, web browser manufacturers tried to grab market share by introducing features that would only work on their browser. If you wanted blinking text you had to use Netscape. Of course, in those days blinking text was seen as pretty whizzy! Website developers had a number of unsatisfactory choices: to build a site that worked in only one browser, to build multiple versions of a site, or to build very simple - but dull - sites that didn't use any proprietary code.
As the web developed things began to change; browser manufacturers started to adopt a standard set of codes and procedures which allowed web developers to build sites that would work across different browsers. Old habits die hard though, and most web developers are still building sites the old way, despite the proliferation of standards compliant browsers.
Benefits of Web Standards
Why should you, as a website owner, care about web standards? Isn't one sort of code just as good as another? Absolutely not: although you don't need to know the technical ins and outs - that's the job of your web developers - standards compliant sites have a host of built-in benefits that you'll be really interested in.
Fast-loading pages that cost you less
Pages built using web standards such as CSS (Cascading Style Sheets) usually have much smaller file sizes, as the code tends to be simpler. Your user's browser not only has to download less data, it has to do less work translating the page.
It's not only the user who benefits from smaller file sizes. For popular sites, web hosts often charge for the amount of bandwidth used - the amount of data you transfer - so smaller files mean lower costs. Some websites have switched to CSS based layout for the bandwidth savings alone.
Simpler pages that cost you less
Pages built to web standards tend to have simpler code, so they can be easier to build and maintain. The power of CSS lies in the way they separate presentation from content. This means that site-wide design changes only need to be made in one place - the style sheet - rather than every page of the site. This separation also makes it easier to have different people working on different aspects of the site at the same time. Reduced development times mean reduced cost which can only be good news for site owners.
Sites are often so poorly coded that only the original developer understands them, and if they were to go out of business you'd need to hand the site over to another developer. It can be extremely difficult to decipher the hacks and workarounds used by other developers; it's often quicker to rewrite the site from scratch.
Having a standards compliant site is like a kite mark for code. It shows it was written to a specification that any competent web designer can understand. This frees you from supplier dependency and from spiralling costs where a change of developer is forced on you.
Pages that get found
Pages built using web standards - and in particular those using CSS for layout - are inherently more attractive to search engines. Search engines work by looking at the code of a page and extracting the content. If the code is clean, simple and bug free, it's easy for the search engines to view the content and rank your site.
Search engines have problems with pages containing superfluous or non-standard code. As most web designers still don't use web standards, many sites fail to achieve decent rankings. A whole specialism - search engine optimisation - has sprung-up to help rewrite badly coded pages but this wouldn't be necessary if the site was built properly in the first place.
Pages that are Accessible
Alternative web browsing devices are becoming more common and include things like mobile phones and PDAs (Personal Digital Assistants). In addition many disabled people use assistive technology such as screen readers (used by the visually impaired). One of the aims of web standards is to allow sites to be accessed regardless of the device being used.
It makes sense to have a website that can be used by as many people as possible but making your site accessible to users with disabilities is a legal responsibility for anyone providing a 'service' online. According to the Disability Discrimination Act, since 1999 "service providers have had to consider making reasonable adjustments to the way they deliver their services so that disabled people can use them." Having a web standards compliant site is one of the best ways of meeting this legal requirement.
Standards are the future of the web
Using web standards is the only way to ensure that your site will be compatible with future browser versions. A broken site could cost you dearly in terms of lost sales, damaged reputation and maintenance. A standards compliant site will work across existing and future browsers.