PCT International Search and Preliminary Examination Guidelines
PART III EXAMINER CONSIDERATIONS COMMON TO BOTH THE INTERNATIONAL SEARCHING AUTHORITY AND THE INTERNATIONAL PRELIMINARY EXAMINING AUTHORITY
A13.13 Under the practice of some Authorities, a document whose content alone calls into question the inventive step of at least one independent claim, and possibly that of one or more claims depending on it would be categorized as “X”. The following are examples of situations in which this may occur:
(i) where a technical feature known in a technical field is applied from its original field to another field and its application therein would have been obvious to a person skilled in the art;
(ii) where a difference between the document’s content and the claimed matter is so well known that documentary evidence is unnecessary;
(iii) where the claimed subject matter relates to the use of a known product, and the use would have been obvious from the known properties of the product;
(iv) where the claimed invention differs from the known art merely in the use of equivalents that are so well known that the citation of documentary evidence is unnecessary.