Missing constraints for MR-6Wheel-(non)-lav-composite

[Vladki]

The Midland railways 6-wheel composite carriages (both -lav- and -non-lav-) can be coupled only with other 6-wheelers defined in mr-31ft-arc-carriages.dat.
However the non-composite carriages can be coupled with plenty of other midland railways carriages defined in files:

mr-31ft-arc-carriages.dat
mr-31ft-clerestory-carriages.dat
mr-33ft-6-clerestory-carriages.dat
mr-43ft-arc-carriages.dat
mr-43ft-clerestory-carriages.dat
mr-48ft-arc-carriages.dat
mr-48ft-clerestory-carriages.dat
mr-50ft-arc-carriages.dat
mr-53ft-arc-carriages.dat
mr-53ft-clerestory-carriages.dat
mr-54ft-clerestory-carriages.dat
mr-54ft-eliptical-carriages.dat
mr-60ft-clerestory-carriages.dat
4wheel-1870s.dat
4-wheel-1870s-sub.dat

In all these files wherever is e.g.:
Constraint[Next][X]=MR-6Wheel-non-lav
it should be followed by
Constraint[Next][Y]=MR-6Wheel-non-lav-composite

(and the same for lavatory composite)

EDIT: I think that some sort of constraint groups (which were discussed already several times), would be really useful.