OnFocusout CSS

onfocusout executes a JavaScript when an input field is about to lose focus. 
Here is an example from https://www.w3schools.com/jsref/tryit.asp?filename=tryjsref_onfocusout

<!DOCTYPE html>
<html>
<body>

Enter your name: <input type="text" id="fname" onfocusout="myFunction()">

<p>When you leave the input field, a function is triggered which transforms the input text to upper case.</p>

<script>
function myFunction() {
  var x = document.getElementById("fname");
  x.value = x.value.toUpperCase();
}
</script>

</body>
</html>
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