<html>
<head>
<script src="https://libs.baidu.com/jquery/1.10.2/jquery.min.js">
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<script>
$(document).ready(function(){
$("p").filter($("div p.intro")).css("background-color","yellow");
});
</script>
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<body>
<div style="border:1px solid black;">
This is a div element
<h1>Welcome to My Homepage</h1>
<p>My name is Donald.</p>
<p class="intro">I live in Duckburg (will be selected).</p>
<p>My best friend is Mickey.</p>
</div>
<p class="intro">This p element is outside the div element.</p>
<p>This p element is also outside the div element.</p>
</body>
</html>