code: public function set($key, $value)
      {
          Deprecated::method(1.1, MutableBag::class);
  
          $this->items[$key] = $value;
      }
docs: Sets a item by key.
  
  @param string $key   The key
  @param mixed  $value The value
  
  @deprecated since 1.1 and will be removed in 2.0. Use {@see MutableBag} instead.