parental manegment information table masks

Hi people,

Could you help me with libdvdread. I'm working on parental control
feature. I dumped dvd with ifo_dump and got the following table.
I don't understand the meaning of masks for specific title and level.
Kindly please help me.

Parental Manegment Information table
------------------------------------
Number of Countries: 2
Number of VTSs: 5
Last byte: 215
Start byte: 24
Parental Masks for country: US
VMG    0: 0001  1: 0002  2: 0004  3: 0008  4: 0010  5: 0020  6: 0040  7: 0080
VTS  1 0: 0001  1: 0002  2: 0004  3: 0008  4: 0010  5: 0020  6: 0040  7: 0080
VTS  2 0: 0001  1: 0002  2: 0004  3: 0008  4: 0010  5: 0020  6: 0040  7: 0080
VTS  3 0: 0001  1: 0002  2: 0004  3: 0008  4: 0010  5: 0020  6: 0040  7: 0080
VTS  4 0: 0001  1: 0001  2: 0001  3: 0001  4: 0001  5: 0001  6: 0001  7: 0001
VTS  5 0: 0001  1: 0002  2: 0004  3: 0008  4: 0010  5: 0020  6: 0040  7: 0080
Start byte: 120
Parental Masks for country: JP
VMG    0: 0001  1: 0002  2: 0004  3: 0008  4: 0010  5: 0020  6: 0040  7: 0080
VTS  1 0: 0001  1: 0002  2: 0004  3: 0008  4: 0010  5: 0020  6: 0040  7: 0080
VTS  2 0: 0001  1: 0002  2: 0004  3: 0008  4: 0010  5: 0020  6: 0040  7: 0080
VTS  3 0: 0001  1: 0002  2: 0004  3: 0008  4: 0010  5: 0020  6: 0040  7: 0080
VTS  4 0: 0001  1: 0001  2: 0001  3: 0001  4: 0001  5: 0001  6: 0001  7: 0001
VTS  5 0: 0001  1: 0002  2: 0004  3: 0008  4: 0010  5: 0020  6: 0040  7: 0080

Regards,