642. Derogation and contracting out.

Unless provided otherwise in the uniform rules concerning the international carriage of passengers and goods by rail1, any stipulation which, directly or indirectly, would derogate from those rules is null and void, although the nullity of such a stipulation does not involve the nullity of the other provisions of the contract of carriage2. However, a carrier3 may assume a liability greater and obligations more burdensome than those provided for in the rules4, and OTIF member states5 may conclude agreements6 which derogate from the rules for carriage performed exclusively between two stations on either side of the frontier when there