||covers the "Chinese" or Han-Yu set, part of the "Sino-Tibetan" ("Sino-Indian") continental affinity; comprising 1 set of languages (= 16 outer languages) spoken by communities throughout East Asia, centered on the Huang-He ("Yellow River") and Yangtze basins: 79-A HAN-YU including 3 arterial languages: Putonghua (Mandarin); Wu; Yue (Cantonese) The English term "dialect" has in the past been used inappropriately to describe the major components of "Wider Chinese", which are here classified as a net of 16 outer-languages, divided into 69 inner-languages (and subsequently into 429 "dialects", in the Register's usage of that term and on the basis of presently limited knowledge). Although degrees of spoken inter-intelligibility vary greatly within each outer-language, and are generally low among outer-languages, communication within China is facilitated by a common writing system and by the universal teaching of Putonghua (the standard form of "Mainstream Chinese" or so-called 'Mandarin') as the language of national education. Mainstream Chinese, or Putonghua in the wider sense, is the language with the largest number of primary speakers in the world, serving as the official national language of the most populous nation-state. At the end of the 20th century, the title of "most spoken language in the world" can be taken to alternate between Mainstream Chinese and English within each 24-hour cycle, depending on whether China is "asleep" or "awake". Mainstream Chinese is one of two languages in the world to have reached an estimated total of one billion primary plus alternate voices by the end of the 2bd millennium.