Article 5(1) of the Convention of 27 September 1968 on Jurisdiction and the Enforcement of Judgments in Civil and Commercial Matters must be interpreted as meaning that, in the case of a contract of employment in pursuance of which the employee performs his work in more than one Contracting State, the place of performance of the obligation characterizing the contract, within the meaning of that provision, is the place where or from which the employee principally discharges his obligations towards his employer.