protected_composition.php

<?php
class Car
{
  protected $oilLevel;
  
  protected function checkOilLevel()
  {
    echo "oil level checked : ";
    echo $this->oilLevel;
    echo "\n";
  }

  public function thisWorks()
  {
    $car = new Car();
    $car->oilLevel = 'w00t!';

    $car->checkOilLevel();
  }
}

$car = new Car();
$car->thisWorks(); // prints "oil level checked and oil level"