Пример:
Найти все элементы "потомки" формы.
"HTML"
<form>
<div>Form is surrounded by the green outline</div>
<label>Child:</label>
<input name="name" />
<fieldset>
<label>Grandchild:</label>
<input name="newsletter" />
</fieldset>
</form>
"CSS"
body { font-size:14px; }
form { border:2px green solid; padding:2px; margin:0;
background:#efe; }
div { color:red; }
fieldset { margin:1px; padding:3px; }
"Живой пример jQuery"
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<link href="http://slyweb.ru/css/jqueryiframe.css"
rel="stylesheet" type="text/css"/>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.5.0/jquery.min.js"></script>
<script>
$(document).ready(function(){
$("form input").css("border", "2px dotted blue");
});
</script>
</head>
<body class="iframe">
<form>
<div>Form is surrounded by the green outline</div>
<label>Child:</label>
<input name="name" />
<fieldset>
<label>Grandchild:</label>
<input name="newsletter" />
</fieldset>
</form>
</body>
</html>
<style>
body { font-size:14px; }
form { border:2px green solid; padding:2px; margin:0;
background:#efe; }
div { color:red; }
fieldset { margin:1px; padding:3px; }
</style>