CJK Compatibility

CJK Compatibility is a Unicode block containing square symbols (both CJK and Latin alphanumeric) encoded for compatibility with East Asian character sets. In Unicode 1.0, it was divided into two blocks, named CJK Squared Words (U+3300–U+337F) and CJK Squared Abbreviations (U+3380–U+33FF). The square forms can have different presentations when they are used in horizontal or vertical text. For example, the characters (from ボルト) and  (from トン) should look different in horizontal and in vertical right-to-left:

Characters U+337B through U+337E are the Japanese era calendar scheme symbols Heisei (㍻), Shōwa (㍼), Taishō (㍽) and Meiji (㍾) (also available in certain legacy sets, such as the "NEC special characters" extension for JIS X 0208, as included in Microsoft's version and later JIS X 0213). The Reiwa era symbol is in Enclosed CJK Letters and Months (the CJK Compatibility block having been fully allocated by the time of its commencement).

History
The following Unicode-related documents record the purpose and process of defining specific characters in the CJK Compatibility block: