Opel ANTARA 2013 Owner's Manual page 56

54 Seats, restraints
IL = Suitable for particular ISOFIX restraint systems of the 'vehicle-specific', 'restricted' or 'semi-universal' categories.
The ISOFIX restraint system must be approved for the specific vehicle type.
IUF = Suitable for ISOFIX forward-facing child restraint systems of universal category approved for use in this weight and
age class.
X = No ISOFIX child restraint system approved in this weight and age class.
ISOFIX size class and seat device
A - ISO/F3 = Forward-facing child restraint system for children of maximum size in the weight class 9 to 18 kg.
B - ISO/F2 = Forward-facing child restraint system for smaller children in the weight class 9 to 18 kg.
B1 - ISO/F2X = Forward-facing child restraint system for smaller children in the weight class 9 to 18 kg.
C - ISO/R3 = Rear-facing child restraint system for children of maximum size in the weight class up to 18 kg.
D - ISO/R2 = Rear-facing child restraint system for smaller children in the weight class up to 18 kg.
E - ISO/R1 = Rear-facing child restraint system for young children in the weight class up to 13 kg.