Adding Regions to a Theme doesnt mention this will blast away all default regions

[tommym9]

Under Adding Regions to a Theme the docs set out how to declare new regions. It misses off the bit where you need to also re-declare the default regions or they will be disabled.

https://github.com/WidgetsBurritos/d8-studyguide/blob/master/3-front-end-development/3.1-creating-themes.md