HTML Code
<!DOCTYPE html>

<html lang=en>

<head>

  <meta charset=UTF-8>

  <meta name=viewport content="width=device-width,initial-scale=1">

  <title>open — expand all FAQ</title>

  <style>body{font-family:system-ui,sans-serif;margin:0;padding:1.5rem;background:#f8fafc;color:#334155;line-height:1.7}h1{margin:0 0 .75rem;font-size:1.25rem;color:#0f172a}.actions{display:flex;gap:.5rem;margin-bottom:1rem;flex-wrap:wrap}.actions button{padding:.5rem 1rem;border:1px solid #cbd5e1;border-radius:8px;background:#fff;cursor:pointer;font-size:.875rem}.actions button:first-child{background:#2563eb;border-color:#2563eb;color:#fff}details.faq{margin-bottom:.5rem;padding:.75rem 1rem;border:1px solid #e2e8f0;border-radius:8px;background:#fff;max-width:420px}summary{cursor:pointer;font-weight:600}#status{margin-top:.75rem;font-size:.875rem;color:#64748b}</style>

</head>

<body>

  <h1>Expand / collapse all</h1>

  <div class=actions>

    <button type=button id=expandBtn>Expand all</button>

    <button type=button id=collapseBtn>Collapse all</button>

  </div>



  <details class=faq>

    <summary>What is HTML?</summary>

    <p>HTML structures web page content.</p>

  </details>

  <details class=faq>

    <summary>What is the open attribute?</summary>

    <p>A boolean attribute on details and dialog.</p>

  </details>

  <details class=faq>

    <summary>Can I toggle open in JavaScript?</summary>

    <p>Yes — set details.open = true or false.</p>

  </details>

  <p id=status aria-live=polite>All panels collapsed</p>



  <script>var status=document.getElementById("status");function setAllOpen(e){document.querySelectorAll("details.faq").forEach((function(t){t.open=e})),status.textContent=e?"All panels expanded":"All panels collapsed"}document.getElementById("expandBtn").addEventListener("click",(function(){setAllOpen(!0)})),document.getElementById("collapseBtn").addEventListener("click",(function(){setAllOpen(!1)}))</script>

</body>

</html>
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HTML open Attribute — expand all FAQ panels
