Test the fix for client-side validation in forms with randomised ids: Place 'testform.php' in your web root and access it Open browser dev tools -> console and make sure 'persist logs' is enabled (or equivalent). Leave the console open. Click on "Collapse me" to collapse the fieldset Click on Submit Confirm that the section was opened Confirm that there is an error immediately below the field Confirm that the field error was focused Confirm that you don't see any JS errors in the console Submit the form again, watching for a browser post. Verify nothing is posted. Reload the page to clear the validation error Click in the text field Press the [tab] key Confirm that there is an error immediately below the field  Regression test 1: Confirming this works for forms without randomised ids (the vast majority of cases in Moodle): Edit 'testform.php' and change: ['data-random-ids' => 1] to: ['data-random-ids' => 0] thus disabling the randomised ids. Repeat all of the previous tests Regression test 2: Confirming client side validation works when multiple forms are used and when randomisation of ids is enabled N.B. This test is based on the test in MDL-65217 , but adds client side validation test steps. Place 'testmultipleforms.php' in your web root and access it Open browser dev tools -> console and make sure 'persist logs' is enabled (or equivalent). Leave the console open. Click on "Collapse me" to collapse the fieldset for both forms Click on Submit Confirm that the section was opened in the form that you submitted Confirm that there is an error immediately below the field Confirm that the field error was focused Confirm that you don't see any JS errors in the console Submit the form again, watching for a browser post. Confirm that there is no entryin the NEtwork tab to suggest that the form was submitted