where in Magento's code are cart rules prossessed

Question

i want to look at the code in magento where the shopping cart rules are checked and applied to the items in the cart before the checkout, i can find in the templates where the information is displayed but i can't find where it is checked if the cart rule should be applied

EDIT 1: by "shopping cart rules are checked" i mean "shopping cart price rules are checked" (maybe there 2 different types of shopping cart rules), i'm looking for the code that goes

"these 3 items that are in the cart meet the conditions of the shopping cart rule with the id of 15, i know need to update the item information as described by the actions provided that the items meet the conditions in the actions"

Answer 1

In the following module: Mage_Salesrule, specifically within app/code/core/Mage/SalesRule/Model/Rule.php

Answer 2

In ver. 1.4.2.0 the main logic about aplying sales rules is in Mage_SalesRule_Model_Validator located in /app/code/core/Mage/SalesRule/Model/Validator.php

Also if you look for Mage::getModel('salesrule/validator') or Mage::getSingleton('salesrule/validator') statements in /app/code/ directory you can see where the rule processing is used:
/app/code/core/Mage/SalesRule/Model/Observer.php
/app/code/core/Mage/SalesRule/Model/Quote/Discount.php
/app/code/core/Mage/SalesRule/Model/Quote/Freeshipping.php