In T 1147/02 the board dealt with the issue of which party to the appeal proceedings bore the burden of proving the exact content of a priority document in order to establish the relevant priority date. Since the appellant was the one to challenge the priority date necessary for establishing prior art, the principles elaborated in the case law of the boards of appeal dictated that the appellant also bore the burden of convincingly proving that the relevant date was not the filing date of the priority document.