PCT International Search and Preliminary Examination Guidelines
PART II THE INTERNATIONAL APPLICATION
Chapter 7 Classification of International Applications
Classification When Scope Is Obscure
7.06 When the scope of the invention is not clear, the classification has to be based on what appears to be the invention insofar as this can be understood. It may be necessary to amend the classification, at a later stage, if obscurities are removed by the search, as discussed in paragraph 7.04.