In the search stage of a European patent application, a prior art search is conducted “on the basis of the claims, with due regard to the description and the drawings”. Once the claims have been searched, the EPO can be very reluctant to allow an amendment to the claims if that amendment relates to subject-matter outside the scope of the search that has been conducted. It is not an unusual occurrence for applicants to hit a wall with an EPO examiner who is refusing to allow an amendment because it relates to “unsearched subject-matter” under Rule 137(5) EPC. In these cases, to pursue this subject-matter further, the only available strategy is the filing of a divisional application (which can come at significant expense).
In this regard, identifying what kind of amendments the EPO examiners will and will not deem to be “allowable” can be difficult. Decision T1679/10 issued by the EPO Boards of Appeal provides clarification on the criteria for deciding whether an amendment should be refused on these grounds.
In T1679/10, the application as filed related to a system for generating a trick mode stream by data encoding. The description included client-side generation embodiments and server-side generation embodiments. However, the claims as originally filed did not refer to client-side embodiments. Specifically, original claims 1–9 referred to server-side embodiments and original claim 10 was so broadly drafted that it could be construed as either type of embodiment. Nevertheless, in light of claims 1–9, the search division interpreted claim 10 as applying to a server-side embodiment only, and thus their search did not encompass the client-side embodiments.
The applicant later replaced the claims to server-side embodiments with claims toward clientside embodiments. The examining division refused the application on the basis that the new claims were not allowable. The reasoning of the examining division was that the client-side embodiments were not searched, and furthermore that the new set of claims lacked unity of invention with the original claims. The decision was appealed, with the appellant arguing that the examining division had not applied the correct criteria in determining whether the amendments were allowable.
Board of Appeal decision T1679/10 The Board of Appeal disagreed with the conclusion of the examining division that the new claims were not allowable. In doing so, the Board emphasised that to reject an amendment as “unallowable” under Rule 137(5) EPC, two criteria must be fulfilled:
 the amended claims relate to unsearched subject-matter and  the amended claims lack unity of invention with the originally claimed invention or group of inventions.
The Board considered each requirement separately.
Unsearched subject-matter The appellant argued that original claim 10 was broad enough to cover both client-side and server-side embodiments. Thus, the claim should have been construed accordingly and the search should have covered the client-side embodiments.
The Board rejected these arguments of the appellant. The Board agreed with the examining division that, given the broad language of claim 10 and the lack of any dependent claims toward client-side embodiments, the search division could not have reasonably expected the claims to be amended toward client-side embodiments. Thus, these embodiments should not have been searched, and criterion  was fulfilled.
Notably, the EPO Guidelines for Examination state that the search should extend to subject-matter to which the claims might reasonably be expected to be directed after amendment. However, the Board was careful to point out that it would “go too far” to interpret the Guidelines as meaning that it is sufficient to include a single broad independent claim in the claims as originally filed in order to be entitled to a search extending to a large number of embodiments covered by the wording of that claim.
Lack of unity The Board disagreed with the conclusion of the examining division on this point, based on the facts of the case. Principally, the Board concluded that the claims on file included a special technical feature that resulted in the same technical effect as the special technical feature of the claims under appeal – this was the case even a posteriori in light of the prior art. Thus, the original claims and the claims under appeal related to the same inventive concept and there was unity of invention between the two sets of claims. Criterion  was therefore not fulfilled.
Because both conditions were not fulfilled, the Board decided that the examining division had wrongly concluded that the claims were “not allowable”, and the case was remitted back to examination.
Conclusion In T1679/10, the Board reiterated the practice that it is still possible to amend claims toward unsearched subject-matter, so long as that unsearched subject-matter is unitary with the original claims.
However, in practice, making such an argument at a later stage of examination can be difficult if examiners do not correctly apply Rule 137(5) EPC. Therefore we would generally recommend that applicants make sure that the subject-matter they wish to be searched is clearly set out in the claims on file before the EPO commences their search. In particular, providing a consistent set of dependent claims setting out optional features will help clarify to the EPO the nature of the subject-matter to be searched.