Tryit Editor v2.7

Edit This Code:
<!DOCTYPE html>
<html>
<body>

<p>Click the button to create a LEGEND element with some text.</p>

<fieldset id="myFieldset">
  Name: <input type="text">
</fieldset><br>

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

<script>
function myFunction() {
    var x = document.createElement("LEGEND");
    var t = document.createTextNode("Personalia:");
    x.appendChild(t);
    document.getElementById("myFieldset").appendChild(x);
}
</script>

</body>
</html>