Other great resources: Official JS API docs, Scripting Forum
DEFENSE
any type of base defence (eg. pit, bunker, hardpoint, etc) but also includes sensors, ECM towers and radar detector towers.
really hope the sensors/etc get split out in to their own types at some point!
you can get more accurate idea of what type of structure it is using .name property of Structure object - that object also has properties like .canHitAir, etc.