How to create a view area handler I'm building a Drupal Commerce store. On cart view I need to display some additional information.

I want to create area handler like Commerce Order: Total. It should do some php logic and display the results. 

Can anybody give me some advice how to build such a handler? The documentation didn't gave me much information.
You need to create a custom module and override default area handler using hook_views_data_alter().

The default implementation of order total handler placed here.