The WHO ICD-10 scheme chapters. The chapter level is the highest in the hierarchy, each chapter containing sets of codes which span multiple three-digit 'major' codes, and in some cases also span codes across two alphabetic initial characters. E.g. Chapter I spans A00 to B99.
2017 ICD-10-CM does not have any U codes (codes for special purposes). U00-U49 - Provisional assignment of new diseases of uncertain etiology or emergency use U82-U85 - Resistance to antimicrobial and anti-neoplastic drugs
Format: list with chapter names stored in list names, each with two element named character vector with start and end codes.