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UTF-8, a transformation format of Unicode and ISO 10646 (RFC2044)

IP.com Disclosure Number: IPCOM000002599D
Original Publication Date: 1996-Oct-01
Included in the Prior Art Database: 2019-Feb-16
Document File: 6 page(s) / 8K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

F. Yergeau: AUTHOR

Related Documents

10.17487/RFC2044: DOI

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. UTF-8, the object of this memo, has the characteristic of preserving the full US-ASCII range. This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 28% of the total text.

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 ([RFC1642]). 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 [Page 1]

RFC 2044 UTF-8 October 1996

US-ASCII characters are encoded in one octet having the normal US- ASCII value, and any octet with such a value can only stand for an US-ASCII character, and nothing else.

UTF-16 is a scheme for transforming a subset of the UCS-4 repertoire into a pair of UCS-2 values from a reserved range. UTF-16 impacts UTF-8 in that UCS-2 values from the reserved range must be treated specially in the UTF-8 transformation.

UTF-8 encodes UCS-2 or UCS-4 characters as a varying number of octets, where the number of octets, and the value of each, depend on the integer value assigned to the character in ISO 10646. This transformation format has the following characteristics (all values are in hexadecimal):

- Character values from...

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