The initial customization project and the initial source code of the extension library for this course:
https://github.com/Acumatica/Help-and-Training-Examples/tree/2019R2/Customization/T230

The reference implementation of the customization described in this course:
https://github.com/Acumatica/Help-and-Training-Examples/tree/2019R2/Customization/T240