@Marty, I’ve used the term “framework” loosely as the library of classes provided by Grav. Most of these classes are documented in the API chapter. It’s nothing but a layer on top of plain PHP, hence the “and/or”.
Everything in Grav (configs, pages) is stored in flat files, which can be manipulated by any app - with or without using Grav’s classes. Admin is optional and isn’t needed at all. You can manage the entire website using vi, vscode, or any other editor.