CPC Combination Sets are groups of CPC symbols linking multiple features of an invention. Patent examiners assign these combination sets in special technical fields to classify different aspects of the main inventive feature. Since July 2017, CPC Combination Sets have been available in DWPI updates. Records from before July 2017 were enhanced with CPC Combination Sets during the course of 2018. Now, CPC Combination Sets are available for all relevant DWPI records, more than 1 million in total (as of the 2019/02 update).
Details about searching and displaying CPC Combination Sets are available online: https://www.cas.org/sites/default/files/documents/cpc_combination_sets.pdf