FPID and Demdex ID in AEP Web SDK

Hi Team,

Adobe product documentation mentions that if we are using FPID in our implementation than we cannot use Use third-party cookies option in Web SDK configuration,

This means I can use either FPID or Demdex ID to seed ECID.

I want to understand what happens if we have both of these options enabled?

• Does to FPID take precedence over Demdex ID or vice-a-versa?
• Does it break the visitor identification process? What happens then? How does user get ECID?
• Does it work like if FPID is available use it otherwise use Demdex ID or vice-a-versa?

Thanks