http://www.rfc-editor.org/rfc/rfc2279.txt
RFC 2279: UTF-8, a transformation format of ISO 10646, F. Yergeau1998-01-01T23:00:00-00:00UTF-8, the object of this memo, has the characteristic of preserving the full US-ASCII range, providing compatibility with file systems, parsers and other software that rely on US-ASCII values but are transparent to other values. This memo updates and replaces RFC 2044, in particular addressing the question of versions of the relevant standards. [STANDARDS-TRACK]