SUMMARY
Run 
<!doctype html>
<head>
   <title>summary tag</title>
</head>
<body>
   <h1> summary tag example!</h1>
   <details>
      <summary>I have keys but no doors. I have space but no room. You can enter but can’t leave. What am I?</summary>
      A keyboard.
   </details>
</body>
</html>