In After Effects cs6 scripting guide, it says that the attribute "numProperties" returns the number of indexed properties within a group of properties, and because of so when it is used with layers it will return a value of 3 corresponding to the groups of "effects", "masks", and "motion tracker".
but whenever i try it with any layer or any group of properties it returns the number of all the children within. this confuses me, makes me work without confidence.