For the first few constants it's supposed to reflect the order in which they're supposed to be set. 1 is a pre-req for 2 which is a pre-req for 4. 4 is a pre-req for 8 and 0x10 (16) although 8 is not a pre-req for 0x10. These are intended for internal use only, hence the `@access private` so it shouldn't cause anyone any problems anyway.