What Does zoom do in CSS

Question

I saw that certain jQuery plugins utilize the "zoom" descriptor in their CSS rules; I even looked it up on the w3c website and discovered that it is used to magnify, but how do I go about doing it? Do I need to define a viewport, though? How can I define a viewport like that, then? Or am I simply mistaken about everything?

is it possible to use it like

a {
    zoom:1;
}

a:hover {
   zoom:2;
}