Checking if a zone is an instance

[Nibiuno]

How can I check if a zone is an instance version or not?

I did a check on quest::GetInstanceID in player.pl when a player enters the zone, but it doesnt work for 100% of cases. This works if the instance returned is greater than 0, but, the issue with that is if a player had an instance and left it, then enters the regular version of that zone before the instance expires, that check reports the instance number of the instance they left.

Is there an easy way to detect if a zone is an instance? I need to signal NPCs if it is, and dont want to if its the regular zone.