The onBeforeValidate handler is used for when an editor saves a piece of content, but before LiveWhale validates the data, you can perform your own custom validation.
(Note, the $id variable will only be populated when saving an existing piece of content. When creating new content, it will be blank.)
To add a validation check, look to the
$_LW->POST array for the submitted values, and add error messages to the
$_LW->REGISTERED_MESSAGES['failure'] array as needed.