Typically, in a microsegmented network, NGFWs are used in conjunction with VLANs to implement security policies and to inspect and filter network communications. Fortinet FortiSwitch and FortiGate NGFW offer an integrated approach to microsegmentation.

The three criteria that a FortiGate device can use to look for a matching firewall policy to process traffic are:
A: Services defined in the firewall policy - FortiGate devices can match firewall policies based on the services defined in the policy, such as HTTP, FTP, or DNS.
D: Destination defined as internet services in the firewall policy - FortiGate devices can also match firewall policies based on the destination of the traffic, including destination IP address, interface, or internet services.
E: Highest to lowest priority defined in the firewall policy - FortiGate devices can prioritize firewall policies based on the priority defined in the policy. The device will process traffic against the policy with the highest priority first and move down the list until it finds a matching policy.

Explanation
https://fortinetweb.s3.amazonaws.com/docs.fortinet.com/v2/attachments/32cb817d-a307-11eb-b70b-0050569258