Commerce Integration - Oppty to CPQ Transaction Import

Summary

How does Oppty-CPQ transaction attribute import works?

Content

Hi,

During the OOTB Commerce Integration for Opportunity- Transaction header, CPQ pulls the Opportunity details to Transaction by querying Opportunity ID (Sales-Opportunity field). 
In the request SOAP XSL, we use the getOpportunity SOAP call and assign optyId (Sales-Opportunity) to opportunityID_t (CPQ Transaction). 

Based on this opportunityID_t, the Opportunity attributes are pushed to CPQ Transaction attributes.

Can someone explain how exactly how this Commerce integration of Opportunity- CPQ Import works.

Thanks
Kavin