(13)As a rule, European specifications are developed in the spirit of the new approach to technical harmonisation and standardisation. They enable a presumption to be made of conformity with certain essential requirements of this Directive, particularly in the case of interoperability constituents and interfaces. These European specifications, or the applicable parts thereof, are not mandatory and no explicit reference to these specifications may be made in the TSIs. References to these European specifications are published in the Official Journal of the European Union , and Member States publish the references to the national standards transposing the European standards.