According to the case law of the boards of appeal, it is possible in particular circumstances, such as in the case of an accidental anticipation of the invention, to introduce a disclaimer in a claim based on a well-defined accidentally novelty-destroying prior art document (cf. eg T 917/94 of 28 October 1999; T 596/96 of 14 December 1999; T 426/94 of 22 May 1996; T 608/96 of 11 July 2000).