[Question] How personalization works technically in Foundation code?

[whuu]

Foundation code uses next.js ISG (incremental static generation) to prebuild the pages and SWR to fetch the content client side.
I have personalized block in my content area, for example use different block based on the audience per country.
How it works from the technical angle:

• How the frontend app knows that it needs to fetch the content on client side (with SWR) to render personalized version?
• Which part of the code does that?