rollover effect

[Sonia]

The following is a code to produce a rolloover effect on a link:
document.all.link.style.color= 'red'

But what does 'document.all' means?

[pyro]

document.all is the IE4 way to reference an element. The DOM way is document.getElementById().

document.all = IE4
document.layers = NN4
document.getElementById() = DOM

So, you'd be better with:

document.getElementById("link").style.color= 'red'

Or, even better, just use CSS in the first place:

<style type="text/css">
.link:hover {
color: red;
}
</style>

[Sonia]

What does DOM mean?

[pyro]

DOM stands for Document Object Module. More info at http://www.w3c.org/DOM/#what