How does FortiExtender connect to FortiSASE in a site-based, remote internet access method?

In FortiSASE site-based (remote internet access) deployments, FortiExtender is used to onboard branch or remote sites without a local FortiGate.

According to FortiSASE and FortiExtender architecture documentation:

FortiExtender integrates with FortiSASE using a secure VXLAN-over-IPsec tunnel

This tunnel:

Extends the site network to FortiSASE

Transparently forwards traffic for inspection

Preserves network segmentation and routing context

This design is similar to cloud-based LAN extension and is not proxy-based

Why the other options are incorrect

B: FortiClient is used for agent-based user access, not FortiExtender

C: Secure Web Gateway (SWG) is a service, not a transport mechanism

D: PAC files and explicit proxies are used in agentless / proxy-based access, not site-based FortiExtender deployments