<!DOCTYPE html>
<html>
<head>
 <title>':lang()': inherit LANG from document HTTP-EQUIV</title>
 <meta http-equiv="content-language" content="z-test">
 <style>
  p:lang(z-test) { background: green }
 </style>
</head>
<body>
 <div>
    <p>This line should have a green background.
 </div>
 <div lang="y-test">
    <p>This line should NOT have a green background.
 </div>
</body>
</html>