DHTML is a mixture of Javascript and HTML in that it uses Javascriptcommands to extend the capabilities of conventional HTML. Earlier,animations were possible using only animated images (animated GIFs, that arean image format) or sophisticated Java programming. Both have drawbacks forthe average Web developer. Animated GIFs use up oodles of space and are slowto download; the image quality is poor. Java programming is beyond the reachof most people who then rely on hand-me-downs from the Web for theiranimations.

Therefore, DHTML. This allows the Web developer to create moving text andpictures on a page, change either or both when somebody does something tothem (moving a mouse over them or clicking) or have real-time transactionssuch as filling up a form and informing people what they have done. What isneeded is an up-to-date Web development tool and a regular knowledge ofHTML.

An example of DHTML is the `Marquee' command, which creates scrolling text.Developers can choose the text to be scrolled, the background colour of thescroll area and the speed of the scroll. At the moment, there are only a fewcommands available for this command, but future specifications of HTML willextend these. It is useful for putting multiple lines of information in thesame spot and have it run repeatedly.

There are still problems with DHTML though. While Microsoft's InternetExplorer 4.01 interprets it fine and does what it is supposed to, Netscape'sCommunicator does not recognise certain DHTML commands.

However, Communicator does recognise the `Layers' command. This letsdevelopers superimpose one page on top of another. This superimposed pagecould be a navigation bar with links to different parts of the site. Or textand pictures. Click on the layer and it minimises to a tab in one corner,ready to be opened at the next click. Layers is another form of Webprogramming and is good for placing many items on a page without clutteringup the works.

Forms, those questionnaires that most commercial sites have on the Internet,are another place where DHTML comes in handy. Suppose on a shopping site, avisitor selects 10 items to place in a shopping basket. He then wants to seewhat he's picked and the cost. All he does is go to the list and scroll downto the items he has selected. The programme automatically generates a totalfor him. If he wants to delete selected items, he can do so and instantlyarrive at another total.

Actually, most good Web pages now use a combination of DHTML and Javascript.This gets around the problem of Netscape not recognising DHTML and isspecially pertinent in applications that are important -- a shopping basket,for example. While DHTML will make the page interact with users on InternetExplorer, you will need a dose of Javascript to make it run on Netscape. Ina way, they complement each other.

Image animation can also be done using DHTML. Essentially, Web developerscan create something similar to a slide show using this language. Theprogramming places a sequence of images on a particular place on the pagethat change in a predetermined manner -- dissolving, cutting, wiping -- fromone to another. This helps save on download time for the page as well asspace on the page. Image animation done this way looks similar to that whichcan be achieved via animated GIFs. The difference is that DHTML animationloads images one after the other, while an animated GIF sequence loads allat once. This means that a DHTML animation will show the first image fastand the others when all have loaded, while the animated GIFs will not showat all until all have loaded. However, as DHTML does not work on Netscape,all visitors will see is the first image; this problem does not occur withanimated GIFs.

Also available are Java programmes that let animations be created, whichgive the same effect as animated GIFs. These have an advantage over eitherDHTML animations in that they work on all browsers. They are also betterthan animated GIFs in that the image quality is better and there are avariety of transitions between images. However, this article does not gointo the details of Java animations.

Web developers can strike a nice balance between using DHTML fornon-critical applications and Java or Javascripting for critical ones on apage. This way, people using Internet Explorer see the page in all itsglory, while Netscape users see a somewhat pared down version of the samething. However, if both have been used judiciously, no visitor, irrespectiveof the browser he is using, need be deprived of the contents of the page.