how is "save" defined

I am almost done with this script, but cannot seem to find the function definition of save- can someone help?  My goal is this:

Upon clicking "save" on an SO, I want this script to take the total of the SO, add it to the current balance, and if it exceeds the credit limit on the customer form, block the save to error.

Here is what I have:

To be run when ‘save’ is selected





function noCreditKillSave()

{
            var creditLimit = nlapiGetFieldvalue('creditlimit');

            var balanceAmount = nlapiGetFieldvalue('balance');

            var totalAmount = nlapiGetFieldvalue('total');

           

            if( (balanceAmount + totalAmount) >= creditLimit)

            {

                        //need to kill the 'save' process