noun
code extension character
Technical term in character encoding standards; used to switch between character sets or control functions.
ISO/IEC 2022では、コード拡張文字を使って文字集合を切り替える。
In ISO/IEC 2022, code extension characters are used to switch character sets.
Compound of コード (code) + 拡張 (extension) + 文字 (character), likely a calque from English 'code extension character' used in character encoding standards.