Tooltips! They pop up wherever your mouse is, thanks to some clever javascript (I ended up pulling it out of Loduwijk's KeyState library, and tweaking it):
update_mouse()
src << output({"
<html>
<head>
<script type="text/javascript">
function coordinate(event)
{
window.location="?action=mousecoord&x="+event.screenX+"&y="+event.screenY
}
</script>
</head>
<body onload="coordinate(event)">
</body>
</html>
"},"window1.browser1")
Much thanks to Koil for actually writing the tooltip part of the code and saving me soooooo much time.