Under Art. 88(4) EPC 1973 it suffices if the features claimed in the later application are disclosed by the earlier application taken as a whole (T 497/91, T 184/84 and T 359/92). Art. 88(4) EPC 1973 cannot be construed as meaning that a priority document must comprise claims in order to form a regular national filing within the meaning of Art. 87(3) EPC 1973 which can give rise to a right of priority. If the priority document does not include any claims, this does not mean that the conditions of Art. 88(4) EPC 1973 are not fulfilled (T 469/92). Features of the invention may also be disclosed in the drawings (T 169/83, OJ 1985, 193).
On the other hand, T 409/90 (OJ 1993, 40), showed that a broad claim in the previous application was not necessarily a suitable basis for a priority right. This decision was based on the principle that what was disclosed by a priority document was what could be deduced from the priority document as a whole by a person skilled in the art. However, when considering what was disclosed in a priority document's claim it was necessary to bear in mind the purpose of the claim, i.e. to define the protection sought. The fact that a claim in a priority document was broad enough to cover specific subject-matter filed for the first time in a later application was not by itself sufficient evidence that such subsequently filed subject-matter had already been disclosed in the priority document, or that subsequent claims based on the later-filed subject-matter still defined the same invention as that which was the subject of the priority document (see also T 77/97).
At issue in T 289/00 was whether the feature in Claim 1, namely that a channel was enclosed on all sides, was directly and unambiguously disclosed in the priority application. The board accepted that the latter's reference to the channel as "filled with air" did not in itself mean that it was enclosed. However, under Art. 88(4) EPC 1973 the previous application's documents had to be considered as a whole, and the reference therefore had to be seen together with the other information on this matter which the skilled person would derive from the application. A skilled person considering the priority application documents as a whole would conclude, without further information, that the channel would be enclosed on all sides.
In T 515/00 the board noted that a claim passed the priority test if its subject-matter could be derived from the previous application as a whole. It followed that comparing the claim with the corresponding claim of the previous application was not a valid approach to performing the "priority test".