3d flash

Hi All
I have beem reading and reading and reading again, and trying to understand the tutorial senocular made about 3d in flash, but still have some things i didnt understand completely, do you mind if i ask some of those here?

FOIR EXAMPLE, this is not in the tutorial…but this thing is
I saw in a place, i dont know where , that if we are not seeing the thing we should not renderize it, and it sounds very logical, but the question is:How flash knows the camera is seeing some thing so he can renderize it or not?