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<!DOCTYPE html>
<html>
<body>

<h3>A demonstration of how to access a FIELDSET element</h3>

<fieldset id="myFieldset" name="personalia">
  Name: <input type="text" name="username"><br>
  Email: <input type="text" name="usermail"><br>
</fieldset>

<p>Click the button to disable the fieldset.</p>

<button onclick="myFunction()">Try it</button>

<script>
function myFunction() {
    var x = document.getElementById("myFieldset");
    x.disabled = true;
}
</script>
</body>
</html>