The following style rule selects elements that use the "special" attribute.
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Strict//EN">
<html>
<head>
<style>
.test { display:none; }
[special] { display:block; }
</style>
</head>
<body>
<div class="test" special>Test for [] (Existence) succeeded.</div>
</body>
</html>