A number of non-limiting examples will illustrate where a restriction of the search may find application:
One example would be a claim so broadly formulated that at least part of its scope is speculative, i.e. not supported by the disclosure of the application. In this case the broadness of the claim is such as to render a meaningful search over the whole of the claim impossible, and a meaningful search can be performed only on the basis of the narrower, disclosed invention, for example only on the basis of that part of the claim which is supported. In extreme cases, this may mean a search directed to only one or more of the specific examples disclosed in the description. The examiner should bear in mind that the requirements under Art. 5 and 6 concerning sufficiency of disclosure and support should be seen from the perspective of the person skilled in the art.
An example would be where there are so many claims, or so many possibilities within a claim, that it becomes unduly burdensome to determine the matter for which protection is sought (for the case of multiple independent claims in the same category see GL/PCT‑EPO B‑VIII, 4). A complete search (or any search at all) may de facto be impossible.
It is noted that the EPO allows multiple dependent claims, provided that they do not detract from the clarity of the claims as a whole and that the arrangement of claims does not create obscurity in the definition of the subject-matter to be protected (see also GL/PCT‑EPO F‑IV, 3.4). In case of unclarity, it may be appropriate for the examiner to first invite the applicant for informal clarification before the search is carried out (see GL/PCT‑EPO B‑VIII, 3.3-3.6).
An example would be where the applicant's choice of parameter to define the invention renders a meaningful comparison with the prior art impossible, perhaps because the prior art has not employed the same parameter, or has employed no parameter at all. In such a case, the parameter chosen by the applicant may lack clarity (see Art. 6; cf. GL/PCT‑EPO F‑IV, 4.11). It may be that the lack of clarity of the parameter is such as to render a meaningful search of the claims or of a claim or of a part of a claim impossible, because the choice of parameter renders a sensible comparison of the claimed invention with the prior art impossible. If so, the search may possibly be restricted to the worked examples, as far as they can be understood, or to the way in which the desired parameter is obtained.
In all examples listed above, the examiner may where appropriate informally invite the applicant to provide clarification of the claimed subject-matter (see GL/PCT‑EPO B‑VIII, 3.3).