<html>
<head>
<script type="text/javascript" src="jquery.js"></script>
</head>
<body>
<ul>
  <li><strong>list</strong> item 1 -
    one strong tag</li>
  <li><strong>list</strong> item <strong>2</strong> -
    two <span>strong tags</span></li>
  <li>list item 3</li>
  <li>list item 4</li>
  <li>list item 5</li>
  <li>list item 6</li>
</ul>

<script type="text/javascript">
$('li').filter(function(index) {
  return $('strong', this).length == 1;
}).css('background-color','red');
</script>

</body>
</html>

Given the HTML above, what's the meaning of the comma in the selector below?

return $('strong', this).length == 2;

What will happen if I remove the word 'strong'?

javascript jquery jquery-selectors
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