By "preclassification" is meant a first stage of routing, for purposes of internal handling, whereby the subject of the claimed invention (or the invention first claimed, if there is more than one) is broadly identified by means of the appropriate classification symbols. By "official classification" is meant the assigning of the appropriate classification symbols identifying the technical subject of the claimed invention (or of the subjects of each of the claimed inventions, if there is more than one), such identification being as precise and comprehensive as the classification permits. In addition, non-obligatory classification or indexation symbols may be attributed to any additional information contained in the document to be classified, which should be identified according to the Guide to the International Patent Classification ("IPC") published by WIPO (see also the WIPO website). The official classification of the European patent application is performed by the examiner, using the classification symbols contained in the rules of the IPC for the inventions as claimed ("Obligatory Classification"). He can also assign appropriate classification symbols and/or indexing codes to any additional information ("Non-Obligatory Classification") as defined in the Guide to the IPC in force at the time.