The search is carried out in collections of documents or databases which may contain material in all those technical fields pertinent to the invention. The search strategy determines the sections of the documentation to be consulted covering all directly relevant technical fields, and may then have to be extended to sections of the documentation covering analogous fields, but the need for this must be judged by the search division in each individual case, taking into account the outcome of the search in the sections of the documentation initially consulted (see B‑III, 3.2).

The question of which technical fields are, in any given case, to be regarded as analogous has to be considered in the light of what appears to be the essential technical contribution of the invention and not only the specific functions expressly indicated in the application.

The decision to extend the search to fields not mentioned in the application must be left to the judgement of the search division, which does not put itself in the place of the inventor and does not try to imagine all the kinds of applications of the invention possible. The overriding principle in determining the extension of the search in analogous fields is whether it is probable that a reasonable objection of lack of inventive step could be established on the basis of what is likely to be found by the search in these fields (see T 176/84, T 195/84 and G‑VII, 3).