Line of Sight
Source Player Core pg. 419
Some effects require you to have line of sight to your target. As long as you can precisely sense the area (as described in Perception) and it isn't blocked by a solid barrier (as described in Cover), you have line of sight. An area of darkness prevents line of sight if you don't have darkvision, but metal gates and other obstacles that aren't totally solid don't. Usually a 1-foot-square gap is enough to maintain line of sight, though the GM makes the final call.