What's the difference between Field/LevelField/ArrayLevelField?

[TheXs]

Hi，there: Just got a bit confused about the difference between those files ended with Field/LevelField/ArrayLevelField. I can see LevelField apparently contain more fields. My question is: how do we qualify a enum(Type in Field files) as a Field Type or a LevelField Type? I'm kind of new in War3 developing . Thanks for any reply! Best Regards!