are grouped into 16 layers of 6 planes each (except for layer 16, which contains the four planes 91–94). Layer 1 contains both non-hanzi and hanzi characters, with the non-hanzi and most frequently used hanzi being placed in plane 1, and with the remaining five planes consisting of less common hanzi. Layer 2 contains simplified Chinese characters, with their row and cell numbers being the same as their traditional Chinese equivalents in layer 1. Layers 3 through 12 contain further variant forms, at row and cell numbers homologous to the first two layers. The last four layers are used for other purposes. Specifically, layer 13 contains additional characters for Japanese language support (kana and Japanese kokuji), and layer 14 contains additional characters for Korean language support (hangul). Layer 15 is unused (reserved), while layer 16 is used for other characters. This distinctive design has been criticized by Christian Wittern of the International Research Institute for Zen Buddhism at Hanazono University, who asserts that the relationship of character variants "is very complex and can not be expressed in a fixed, one-dimensional, hard-wired codetable". Ken Lunde describes it as "one of the most well thought-out character set standards from Taiwan", describing its structure as "to be truly admired", but concluding that OpenType variant form substitution can provide the same level of functionality. CCCII defines roughly 53940 code points as of its 1987 edition, although a more recent draft from 1989 extends this to 75684 code points (comprising 44167 unique characters and 31517 variants). EACC, the variant used by the Library of Congress, includes only a smaller set of 15686 characters. Adoption As of 1995, CCCII or EACC was used mostly in libraries in the United States, Hong Kong and Taiwan. Although CCCII promised pan-CJK coverage, its support was limited to specialized hardware; difficulty ascertaining when the root versus variant character should be used, exacerbated by a lack of firmly established reference glyphs, further limited its adoption, resulting in Big5 being more commonly used for Chinese in those territories outside of library use (since Unicode had yet to become widely adopted at the time). , EACC is still in extensive use for specialized bibliographic purposes. It was also an important precursor to Unicode. Unicode hanzi characters are referenced to their corresponding CCCII and EACC codes in the Unihan database, in the keys and . Mapping tables for hanzi, hangul, kana and punctuation between