How to use add_to_cart () method in WooCommerce?

I am currently adding a product to my cart:

$woocommerce->cart->add_to_cart( $product_id, $quantity );

      

        
        
        
      

    

I noticed that the method add_to_cart()

actually takes 5 parameters. See the following (taken from the WooCommerce docs):

add_to_cart( string $product_id, string $quantity = 1, integer $variation_id = '', array $variation = '', array $cart_item_data = array() )

      

        
        
        
      

    

Can anyone provide an example of what the last 3 parameters will be used for?

• $variation_id
  
  
• $variation
  
  
• $cart_item_data
  
  

There is some description that they are in the documentation for the method, but this is not very explicable:

int $ variant_id

the values ​​of the $ value $ array attribute

array $ cart_item_data additional cart item data that we want to pass to the item

Link: http://docs.woothemes.com/wc-apidocs/class-WC_Cart.html#_add_to_cart