be created as late as the late 19th century, when a number of characters were coined in the Meiji era for new scientific concepts. For example, some characters were produced as regular compounds for some (but not all) SI units, such as ( "meter" + "thousand, kilo-") for kilometer, ( "liter" + "thousand, kilo-") for kiloliter, and ( "gram" + "thousand, kilo-") for kilogram. However, SI units in Japanese today are almost exclusively written using rōmaji or katakana such as or for km, for kl, and or for kg. In Japan, the kokuji category is strictly defined as characters whose earliest appearance is in Japan. If a character appears earlier in the Chinese literature, it is not considered a kokuji even if the character was independently coined in Japan and unrelated to the Chinese character (meaning "not borrowed from Chinese"). In other words, kokuji are not simply characters that were made in Japan, but characters that were first made in Japan. An illustrative example is . This spelling was created in Edo period Japan from the ateji (phonetic kanji spelling) for the existing word ankō by adding the radical to each character—the characters were "made in Japan". However, is not considered kokuji, as it is found in ancient Chinese texts as a corruption of (魚匽). is considered kokuji, as it has not been found in any earlier Chinese text. Casual listings may be more inclusive, including characters such as . Another example is , which is sometimes not considered kokuji due to its earlier presence as a corruption of Chinese . Kokkun In addition to kokuji, there are kanji that have been given meanings in Japanese that are different from their original Chinese meanings. These are not considered kokuji but are instead called kokkun () and include characters such as the following: Types of kanji by category Han-dynasty scholar Xu Shen in his 2nd-century dictionary Shuowen Jiezi classified Chinese characters into six categories ( liùshū, Japanese: rikusho). The traditional classification is still taught but is problematic and no longer the focus of modern lexicographic practice, as some categories are not clearly defined, nor are they mutually exclusive: the first four refer to structural composition, while the last two refer to usage. Shōkei moji () Shōkei (Mandarin: xiàngxíng) characters are pictographic sketches of the object they represent. For example, is an eye, while is a tree. The current forms of the