This project is at the core of creation of Zest Scripts. The project is written in Java as some modules from ZAP have been used.
Working of this project (with Code details) is explained here : https://github.com/owtf/zest-owtf/wiki/How-it-works
For more information : OWTF : https://github.com/owtf/owtf
Mozilla Zest : https://github.com/mozilla/zest