Found this page that is a nice resource for XPath development.

Starting to run a migration from Drupal 7 to 8 using the tutorial/documentation found here:

UPDATE: I ran into trouble with this but GOOD NEWS! This tutorial works great! I was only having issues because the project I working didn’t have the proper networking and infrastructure to support remote development. In other words, the company was too locked down with security and it was difficult to do anything outside of using MS Word… LOL!

This tutorial is great and very straight forward but you do need to be on an unrestricted network. Good luck! I recommend this link!

Migration from Drupal 7 to Drupal 8