The basic test to determine whether a claim is entitled to the date of a priority document is, as far as the requirement of "the same invention" is concerned (see F-VI, 1.3(iv)), the same as the test for determining whether or not an amendment to an application satisfies the requirement of Art. 123(2) (see H-IV, 2). That is to say, for the priority date to be valid in this respect the subject-matter of the claim must be directly and unambiguously derivable from the disclosure of the invention in the priority document, also taking into account any features implicit to a person skilled in the art in what is expressly mentioned in the document (see G 2/98). As an example of an implicit disclosure, a claim to an apparatus including "releasable fastening means" would be entitled to the priority date of a disclosure of that apparatus in which the relevant fastening element was, say, a nut and bolt, or a spring catch or a toggle-operated latch, provided the general concept of "releasable" is implicit in the disclosure of such element. An example of where the subject-matter is not directly and unambiguously derivable is when the claim is directed to a specific numerical range of values and the priority application discloses a different numerical range of values, even if this latter range overlaps with or is comprised within the previous one. In such a case, the claimed amounts represent a continuum of a numerical range of values which does not correspond to distinctive, alternative embodiments (i.e. elements in the sense of Art. 88(3)). Therefore no separable alternative embodiments which could enjoy the right of priority are identifiable within that continuum (T 1877/08).
It is not necessary that the subject-matter for which priority is claimed be found among any claims in the previous application. It is sufficient that the documents of the previous application taken as a whole "specifically disclose" such subject-matter. The description and any claims or drawings of the previous application should, therefore, be considered as a whole in deciding this question, except that account should not be taken of subject-matter found solely in that part of the description referring to prior art, or in an explicit disclaimer.
The requirement that the disclosure must be specific means that it is not sufficient if the subject-matter in question is merely referred to in broad and general terms. A claim to a detailed embodiment of a certain feature would not be entitled to priority on the basis of a mere general reference to that feature in a priority document. Exact correspondence is not required, however. It is enough that, on a reasonable assessment, there is in substance a disclosure of all the subject-matter of the claim.
A disclaimer which is allowable under Art. 123(2) (see H-V, 4.1 and H-V, 4.2) does not change the identity of the invention within the meaning of Art. 87(1). Therefore, such a disclaimer could be introduced when drafting and filing a successive European patent application, without affecting the right to priority from the first application not containing the disclaimer (see G 1/03, G 2/03 and G 2/10).