Forum Moderators: open
have you considered using the title attribute?
example
He fell down a <span title="nearly vertical shaft in a glacier, formed by surface water percolating through a crack">moulin</span>
birdbrain
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>Untitled</title>
<meta http-equiv="content-type" content="text/html; charset=iso-8859-1">
<style type="text/css">
a{display:block;position:relative;}
a span{position:absolute;display:block;visibility:hidden;top:1.2em;left:4em;border:3px groove;background:#dee;}
a:hover{text-indent:0;}
a:hover span{display:block;visibility:visible;}
</style>
</head>
<body>
<p>
<a href="#">
Text to mouseover
<span>popup</span>
</a>
</p>
</body>
</html>