A patent classification is a system for examiners of patent offices or other people to categorize (code) documents, such as published patent applications, according to the technical features of their content. Patent classifications make it feasible to search quickly for documents about earlier disclosures similar to or related to the invention for which a patent is applied for, and to track technological trends in patent applications. Searches based on patent classifications can identify documents of different languages by using the codes (classes) of the system, rather than words.