Standard proxy.pac rules can define a list of proxies but if you need to using a list of specific proxies for a defined domain, you need to use the 4.30 with Service Pack 173 or above.
The 4.30 with Service Pack 173 or above allows you to define a list of proxy for a specific object
- Use the "Force" section inside your proxy.pac rule.
- Create an object and set your records (example: Web server or domain )
- Choose the tab “Proxy servers”
- Add your proxy server inside the list.
- Compile your rule.
It means if the object matches, the proxy.pac will force the browser to use defined proxies directly in the group object.
If it not matches, then browser will continue to use the rule.