RFC 4042:UTF-9 and UTF-18 Efficient Transformation...
RFC-Ref

ISO 10646


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... which is only suitable for [US-ASCII] (although it has been used for various ISO 10646 national variants). To maximize international and multi-lingual interoperability ...


... Hoffman, P. and F. Yergeau, "UTF-16, an encoding of ISO 10646", RFC 2781, February 2000. ...



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