"Where" is a protected property

API page: https://api.drupal.org/api/drupal/core%21modules%21views%21views.api.php...

In the example code we have $query->where but "where" cannot be used in a hook_views_query_alter because it's a protected property:

Error: Cannot access protected property Drupal\search_api\Plugin\views\query\SearchApiQuery::$where