A proper field of search normally includes the classification locations in which the claimed subject matter of an application would be properly classified at the time of the application’s classification or grant of a patent. However, if the above proper classification does not correspond to the subject matter found in the claims (e.g., a situation where the proper classification corresponds to a disclosed, but unclaimed, embodiment), it is not necessary to search areas in which it could reasonably have been determined that there was a low probability of finding the best reference(s).
In outlining a field of search, the examiner should note every classification location (i.e. group/subgroup of the Cooperative Patent Classification or class/subclass of the U.S. Patent Classification) under the utilized classification system and other organized systems of literature that may have material pertinent to the subject matter as claimed, including those which have been assigned by a foreign Office, another USPTO examiner, or by the classification contractor. Every subclass, digest, and cross-reference art collection pertinent to each type of invention claimed should be included, from the largest combination through the various subcombinations to the most elementary part. The field of search should extend to all probable areas relevant to the claimed subject matter and should cover the disclosed features which might reasonably be expected to be claimed. The examiner should consult with other examiners and/or supervisory patent examiners, especially with regard to applications covering subject matter unfamiliar to the examiner.
The areas to be searched should be prioritized so that the most likely areas of finding relevant prior art are searched first. For documenting the field of search see MPEP § 719.05. See MPEP § 1302.10 for search information printed on the face of a patent.