Hook : page.update:before... exemple?

Kirby 3 Questions 🤔
1

This hook is fine :

'page.update:after' => function ($newPage, $oldPage) {
	if($newPage->pourcentage()->isNotEmpty()) {
            $p        = $newPage->pourcentage()->toFloat();
            $items    = site()->index()->filterBy('template', 'product');
            $log      = $newPage->log();

            foreach($items as $item) {
              $prix  = $item->prix()->toFloat();
              $prix  = $prix+($prix*$p/100);

              try {
                  $item->update([
                    'prix'        => $prix
                  ]);
               } 
              catch(Exception $e) { echo $e->getMessage(); }
            }

            $log = $log."\n".date('Y-m-d H:i')." : +".$p."%";

            try {
                  $newPage->update([
                    'pourcentage'         => '',
                    'log'                 => $log
                  ]);
             }
            catch(Exception $e) { echo $e->getMessage();  }
          }
        }

I need to try the same operation with ‘page.update:before’ … but I don’t understand how it works.

'hooks' => [
  	 'page.update:before' => function ($page, $values, $strings) {
    		  $p = $values['pourcentage'];
    		  ... ???
  	 }
 ]

How can i update the fields ? and then the page ?
Thanks :smile: