AJO and content fragments architecture

Hello,

We are looking into using content fragments together with AJO. We found a lot of documentation including a step by step of how to do this in the community here. The content fragment seems to be a reference, since it can also be edited directly from AJO but the documentation states that it is imported here.

My question is : is it imported or a reference to the AEM platform ? 

If it is a reference, does each call to a content fragment count as a content request on the AEM sites licence ?

If it is imported, how is the update managed ?

Thanks in advance !