The problem is that, despite the standards, each browser, version and platform works differently even if only slightly so.
The Extensible Markup Language (XML) and Extensible Style Language (XSL) hold the promise of allowing Web designers to separate the display of content from its actual layout. This will, hopefully, free us from many of the worries of the particular quirks of a browser.
However, despite the recent ratification of a stepping stone to that future in the form of XHTML, browsers continue to be "flawed", at least from a standards point of view.
Recognizing that we live in a flawed World Wide Web, the World Wide Web Consortium has introduced three "flavours" of HTML code in the recently revised HTML 4.01 standard. These three flavors allow Web designers to declare what form their HTML will take: strict, transitional or frameset.
So, I am sure you are scratching your head in wonder, how does the browser know what flavor I am using? Simple, you have to place a <!DOCTYPE> tag at the very top of every Web page, before the tag in fact, to the browser what Document Type Definition (DTD) it should use.
HTML 4.0 Strict The strict form of HTML is nothing but the standard tags HTML 4.01 tags. It's rare that you will see any site - even the W3C's own Web site - using this one. The fact is, standards are great, but no Web browser out there follows them 100 per cent. However, if you are really sure of your coding capabilities, place this tag at the top of your page:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
HTML 4.0 Transitional Transitional HTML is what most people are using now. It includes all of the HTML 4.0 tags, but also allows you to include tags and attributes that are either being "depreciated" (ie, eliminated) from the HTML standard or are used only by a specific browser. Unfortunately, due to incompatibilities between different browser types, some of the power of HTML 4.01 will be sacrificed when using transitional HTML. For example, table elements will not be able to inherit styles and font sizes will very more radically.
More than likely you will want to use the transitional <!DOCTYPE> in your HTML code for the foreseeable future, at least until the overwhelming majority of browsers being used are standards compliant. In theory, the transitional <!DOCTYPE> tag should look like this:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
Unfortunately, this version of the tag still causes IE5/Mac (the only browser to currently make use of the <!DOCTYPE>) to act as if this is strict HTML 4.01 code. This can cause your page to display improperly as I learned the first time I fired my own site up with IE5/Mac. The good news is that there is an easy way around this: take the URL out, thus:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
HTML 4.0 Frameset Finally, frames deserve there own <!DOCTYPE> . If your HTML document is a frameset definition, then you want to use this one:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN" "http://www.w3.org/TR/html4/frameset.dtd">
Validating your pages and !DOCTYPE switching The fact is, however, if you don't add the <!DOCTYPE> to your Web pages, most Web browsers will never notice. However, if you want to check your HTML code for accuracy, by including the <!DOCTYPE> you can then use the W3C's HTML validator to check your code for "accuracy".
Once you have fixed all of these errors you get a nifty "HTML 4.0" button that you can add to the mass of graphics that are cluttering your page. And now your HTML will work everywhere, right. No, not really. Actually, only a very few people surfing the Web right now with anything close to a standards compliant browser, much to many Web designer's chagrin.
But the times they are a changing.
Although currently the only non-beta browser that actually even notices the <!DOCTYPE> tag is IE5/Mac, Navigator 6 and iCab should also make use of it when they are finally released later this year. These programs will use the <!DOCTYPE> tag to validate pages on the fly, allowing the browser to determine the difference between a backwards compatible page (transitional) and a standardised page (strict). This is known as "doctype switching" and will allow standards based browsers to take advantage of the power of HTML 4.01 when the standards are obeyed while still being able to properly render older Web pages.
Jason Cranford Teague is the author of DHTML For the World Wide Web, available from book stores around the UK. If you have questions, you can find an archive of his column at Webbed Environments or email him at email@example.comReuse content