This script makes it simple to automatically-move a user to another field when the cursor reaches the end of the alotted space.
To use the script, add the data-auto-advance-to attribute to the
field you want to advance from and assign the id of the field to
move to:
<input type="text" name="username" required="required"
maxlenght="3" data-auto-advance-to="NEXT_FIELD_ID" />