A push promise extractor for HTML files.
promise_for("""
<html>
<head>
<link rel="stylesheet" type="text/css" href="example.css">
</head>
<body>
<div>
<p></p> <a></a> <p></p>
<img src="http://localhost/example.jpg">
</div>
<div>
<span></span>
</div>
<script src="example.js"></script>
</body>
</html>
""", "http://localhost")
; => ["example.css","http://localhost/example.jpg","example.js"]