A claim may contain undefined, unclear terms for which no clear preferred embodiments are given in the claims but where clear preferred embodiments (i.e. a "fallback position", as referred to in B‑III, 3.2(iv)) of that unclear term are expressed in the description and/or drawings (see B‑III, 3.2.3). In such a case, the search will be based on the broadest technically sensible interpretation of the term. If, however, the meaning of the term in question is so unclear that no meaningful search can be carried out, it is justified to limit the scope of the search according to Rule 63.