Depends how you would like to get the tool tips to appear, and on what kinds of elements. There are mostly two ways I can think of: plain HTML or Javascript/DHTML.

For instance, on many HTML elements you can use the 'title' tag attribute and many browsers will render its value as a tool tip. However, in the past I have used this on image and anchor. Not tried on other elements.

Otherwise, some people may use some Javascript/DHTML that dynamically creates a floating object containing the text at the given mouse location (as captured by the onmouseover event listener). However, this requires the browser with Javascript enabled and the script may be browser-dependent (to some extent). The javascript library listed is an example.

This does not have much to do with Perl, so it is not at all surprising that you are unable to dig anything up in the Perl docs.