RFC 2044 (rfc2044) - Page 1 of 6
UTF-8, a transformation format of Unicode and ISO 10646
Alternative Format: Original Text Document
Network Working Group F. Yergeau
Request for Comments: 2044 Alis Technologies
Category: Informational October 1996
UTF-8, a transformation format of Unicode and ISO 10646
Status of this Memo
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
Abstract
The Unicode Standard, version 1.1, and ISO/IEC 10646-1:1993 jointly
define a 16 bit character set which encompasses most of the world's
writing systems. 16-bit characters, however, are not compatible with
many current applications and protocols, and this has led to the
development of a few so-called UCS transformation formats (UTF), each
with different characteristics. UTF-8, the object of this memo, has
the characteristic of preserving the full US-ASCII range: US-ASCII
characters are encoded in one octet having the usual US-ASCII value,
and any octet with such a value can only be an US-ASCII character.
This provides compatibility with file systems, parsers and other
software that rely on US-ASCII values but are transparent to other
values.
1. Introduction
The Unicode Standard, version 1.1 [UNICODE], and ISO/IEC 10646-1:1993
[ISO-10646] jointly define a 16 bit character set, UCS-2, which
encompasses most of the world's writing systems. ISO 10646 further
defines a 31-bit character set, UCS-4, with currently no assignments
outside of the region corresponding to UCS-2 (the Basic Multilingual
Plane, BMP). The UCS-2 and UCS-4 encodings, however, are hard to use
in many current applications and protocols that assume 8 or even 7
bit characters. Even newer systems able to deal with 16 bit
characters cannot process UCS-4 data. This situation has led to the
development of so-called UCS transformation formats (UTF), each with
different characteristics.
UTF-1 has only historical interest, having been removed from ISO
10646. UTF-7 has the quality of encoding the full Unicode repertoire
using only octets with the high-order bit clear (7 bit US-ASCII
values, [US-ASCII]), and is thus deemed a mail-safe encoding
([RFC 1642]). UTF-8, the object of this memo, uses all bits of an
octet, but has the quality of preserving the full US-ASCII range:
Yergeau Informational