Hello, monks! How to use a line of regular code to get this matter? 
use warnings;
use strict;


my $t = <<'EOF';
<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <script src="CssScriptLoader.js"></script>
    <script src="XZClass.js"></script>
</head>
<div id="224">
<p>aaa</p>
<p>aaa</p>
<p>axxxdsfosdaa</p>
<p>aaa</p>
</div>
<div id="724">
    <p>aaa22</p>
<p>22</p>
<p>22</p>
<p>aaa22</p>
<p>aaa22</p>
<p>aafsdfsdfa22</p>
</div>
<div id="284">
    <p>aaa33</p>
<p>aaa33</p>
<p>aaa33sdfsdfaom</p>
<p>aaa33</p>
<p>aaa33</p>
<p>aaa33</p>
</div>
</html>
EOF

if ($t =~ /<div id="724">(.*?)<\/div>/sg) {
    for my $m ($1 =~ /<p>(.+?)<\/p>/g) {
       print $m, "\n" 
    }
}else {
    print 'match fail!', "\n"
}

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In reply to A line of code matches the question by *2

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