Extending a template from module .. what's the difference between these two methods?

[mzfp]

Hi

I'm experimenting with overriding and extending twig templates from a custom Prestashop module.  

Custom file:
modules/my_module/views/PrestaShop/Admin/Sell/Customer/view.html.twig

In the file above if I place:

{% extends '@PrestaShop/Admin/Sell/Customer/view.html.twig' %}

It crashes the back office - no error - simply runs out of memory.

However, if use the following approach it works:

{% extends '@!PrestaShop/Admin/Sell/Customer/view.html.twig' %}

note that I added the ! operator just before Prestashop.

What is the difference and why does one work and not the other?

[ps8modules]

Hi,

https://github.com/PrestaShop/PrestaShop/issues/29827

https://twig.symfony.com/doc/2.x/tags/extends.html

[mzfp]

Thanks.  Am I correct in my understanding that the not operator (!) ensures that the template is extended from the base template (and another version extended from another module) ?  I read through both links but could not really find a clear explanation of why the ! operator needs to be used.  I'm curious about this