Which Auto load file is used to load default model, helper?

Hi

I am new to Invoice plane and studding the working of Invoice Plane. I was observing the helpers
date_helper.php I notice $CI->mdl_settings->setting(‘date_format’) on line 148. I check at following
places but could not found any reference please help me to understand it better.

/config/config.php
/config.autoload.php

did not find any custom configuration file for it.