[nrser]

Check this fiasco out for starters:

https://github.com/pallets/jinja/issues/659

> It was never documented that you can override variables from higher scopes

But you could, and people did... because that's what people do: they try stuff that seems reasonable and if it works they use it. And then someone "fixed" it in a minor release and things started breaking. BTW the error message is

    KeyError: 'undefined variable: 0'

Fun way to spend an afternoon, I can assure you.

I used Jinja2 happily for years on a web app, but that thing pretty much just styled a page for flash to sit in and drew some forms and menus. I use it now via Ansible and have come to despise it through and through.