For other people trying to initially find out how the remote function works, since I had some issue finding this out initially, here's some sample code.
'validation' => array(
'rules' => array(
'field_id' => array(
'remote' => admin_url( 'admin-ajax.php?action={action_name}' ),
),
),
),
add_action( 'wp_ajax_{action_name}', 'remote_validation' );
function remote_validation() {
echo wp_json_encode( 'true' );
return true;
}
