INTERNET-DRAFT Network Working Group H. Nussbacher Request for Comments: nnnn Israeli Inter-University Computer Center August 1993 Handling of Bi-directional Texts in MIME This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its Areas, and its Working Groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months. Internet-Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet-Drafts as reference material or to cite them other than as a ``working draft'' or ``work in progress.'' To learn the current status of any Internet-Draft, please check the 1id-abstracts.txt listing contained in the Internet-Drafts Shadow Directories on ds.internic.net, nic.nordu.net, ftp.nisc.sri.com, or munnari.oz.au. Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard. Distribution of this memo is unlimited. Abstract This document describes the format and syntax of the "direction" keyword to be used with bi-directional texts in MIME. Description The MIME standards (RFC 1341 and 1342) defined methods for transporting non-ASCII data via a standard RFC822 e-mail system. Specifically, the Content-type field allows for the inclusion of any ISO language such as Arabic (ISO-8859-6) or Hebrew (ISO-8859-8). The problem is that the these two languages are read from right to left and can have bi-directional data such as mixed Hebrew and English on the same line. Nussbacher Expires January 15, 1994 [Page 1] RFC nnnn Hebrew email encodings June 1993 Fortunately, ECMA (European Computer Manufacturers Association) has tackled this problem previously and has issued a technical report called "Handling of Bi-Directional Texts". ECMA TR/53, as it is called, was used to update the Standard ECMA-48 as well as ISO/IEC 6429 (1992). It is based on this information that a new parameter is being defined for MIME Content-type. This new field is called "direction=": Content-type: text/plain; charset=ISO-8859-6; direction=drct or Content-type: text/plain; charset=ISO-8859-8; direction=drct The value of drct can be either implicit, explicit or visual. Implicit Implicit directionality is a presentation method in which the direction is determined by an algorithm according to the type of characters and their position relative to the adjacent characters and according to their primary direction. The complete algorithm is quite complex and sites wishing to implement it should refer to the ECMA Technical Report for further details. Explicit Explicit directionality is a presentation method in which the direction is explicitly defined by using control sequences which are interleaved within the text and are used for direction determination. This presentation method is also defined in ECMA TR/53, which defines three new control functions and updates 22 existing control functions in the ECMA-48 standard. Visual Visual directionality is a presentation method that displays text according to the primary direction only. This is the simplest of all methods and the default method for use with MIME encoded texts. Nussbacher Expires January 15, 1994 [Page 2] RFC nnnn Hebrew email encodings June 1993 References [ECMA TR/53] Handling of Bi-Directional Texts, European Computer Manufacturers Association, 114 Rue du Rhone, CH-1204, Geneva, Switzerland, June 1992 [ISO-6429] [ISO-8859] Information Processing -- 8-bit Single-Byte Coded Graphic Character Sets, Part 6: Arabic alphabet, ISO 8859-8, 1988. [ISO-8859] Information Processing -- 8-bit Single-Byte Coded Graphic Character Sets, Part 8: Latin/Hebrew alphabet, ISO 8859-8, 1988. [RFC822] Crocker, D., "Standard for the Format of ARPA Internet Text Messages", STD 11, RFC 822, UDEL, August 1982. [RFC1341] Borenstein N., and N. Freed, "MIME (Multipurpose Internet Mail Extensions): Mechanisms for Specifying and Describing the Format of Internet Message Bodies", Bellcore, Innosoft, June 1992. [RFC1342] Moore K., "Representation of Non-ASCII Text in Internet Message Headers", University of Tennessee, June 1992. Security Considerations Security issues are not discussed in this memo. Authors' Addresses Hank Nussbacher Computer Center Tel Aviv University Ramat Aviv Israel Fax: +972 3 6409118 Phone: +972 3 6408309 EMail: hank@vm.tau.ac.il Nussbacher Expires January 15, 1994 [Page 3]