“Ctrl+/”
“F11/ESC”
<!DOCTYPE html>
<html>
<body>
<form id="form1">
<button id="button1" type="button">Click me!</button>
</form>
<p>The id of the form containing the button is:
<script>
document.write(document.getElementById("button1").form.id);
</script></p>
</body>
</html>