<input required name="myName" type="text" value="<?php echo $myValue; ?>" class="regular-text">
Does not produce an error message if the field is left blank when I attempt to Update.
What else do I need to do in order to tell the user that this field is required in Gutenberg?
Using the Classic Editor plugin it won't even let me update the page. It presents me with a "!" tooltip that says "Please fill out this field." :)