Menu can still be edited in WordPress Customizer

I really like this plugin. It makes explaining WordPress a lot easier, because for new users it confusing that they need to keep the page hierarchy for permalinks, but also have to manually create a menu structure.

Today I had the situation that somebody somehow managed to ignore the page hierarchy but still have the pages in submenus. I was confused how the person was able to do that and then I found that they can still edit the menu in the WordPress customizer.

To be beginner-proof, I think this plugin should also show a warning when the user tries to edit the WordPress main menu in the customizer.