On the inside of my 2005 XJ8L where the door opener is, there's a round mesh screen. Is this decorative or does it serve a function?

 

If it's anything like my X-Type, that is a tweeter (high frequency speaker) which is part of the audio system.

On the X-Type those come with the premium Alpine audio system whereas the standard system has only the lower door speakers. Sounds like your car should have a pretty nice audio system so enjoy it!

 

Definately the tweeter

 

Thanks for the replies. I suspected as much. The "premium" sound system has all 4 door speakers blown. I looked and I was very surprised that a 2005 had speakers that were paper coned.