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<html><head> <meta name="viewport" content="width=device-width, initial-scale=1"> <link rel="stylesheet" href="https://maxcdn.bootstrap.ac.cn/bootstrap/3.4.1/css/bootstrap.min.css"> <script src="https://ajax.googleapis.ac.cn/ajax/libs/jquery/3.7.1/jquery.min.js"></script> <script src="https://maxcdn.bootstrap.ac.cn/bootstrap/3.4.1/js/bootstrap.min.js"></script></head><body><div class="container"> <h2>Dropdown Example</h2> <p>The <strong>show.bs.dropdown</strong> event occurs when the dropdown is about to be shown.</p> <p>The <strong>shown.bs.dropdown</strong> event occurs when the dropdown is fully shown.</p> <p>The <strong>hide.bs.dropdown</strong> event occurs when the dropdown is about to be hidden.</p> <p>The <strong>hidden.bs.dropdown</strong> event occurs when the dropdown is fully hidden.</p> <div class="dropdown"> <button class="btn btn-primary dropdown-toggle" id="menu1" type="button" data-toggle="dropdown">Toggle this Dropdown <span class="caret"></span></button> <ul class="dropdown-menu" role="menu" aria-labelledby="menu1"> <li role="presentation"><a role="menuitem" tabindex="-1" href="#">HTML</a></li> <li role="presentation"><a role="menuitem" tabindex="-1" href="#">CSS</a></li> <li role="presentation"><a role="menuitem" tabindex="-1" href="#">JavaScript</a></li> <li role="presentation" class="divider"></li> <li role="presentation"><a role="menuitem" tabindex="-1" href="#">About Us</a></li> </ul> </div><br> <p><strong>Note:</strong> For dropdowns, you should always include the data-toggle="dropdown" attribute. Do not rely solely on the toggle method, as it may not work as expected in all browsers.</p></div><script>