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February 1, 2004

Best Practices Document

 

The Printer Working Group

 

 

Best Practices for use of the RepertoireSupported Element

 

Status: Approved

Abstract

In traditional printing environments, clients rely on font downloads when they are not sure a given character is embedded in the printer. As printing moves to small clients, downloading may not be an option and clients have a need to know what characters are available in a given device.

There are many published named character repertoires, and a small client will not know about them all.  

[RS] describes the syntax and semantics for the Semantic Model element "RepertoireSupported".  The current document describes Best Practices for the use of that element, in order to maximize interoperability between client devices and printers.

The reader of this document should be familiar with the terminology and concepts in [RS].

 

Author:
Elliott Bradshaw, Zoran Imaging Division

 

Notices

Copyright (C) 2004, The Printer Working Group. All rights reserved.

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Title:  Best Practices for use of the RepertoireSupported Element

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About the Printer Working Group

The Printer Working Group (or PWG) is a Program of the IEEE-ISTO. All references to the PWG in this document implicitly mean “The Printer Working Group, a Program of the IEEE ISTO.”  The PWG is chartered to make printers and the applications and operating systems supporting them work together better. In order to meet this objective, the PWG will document the results of their work as open standards that define print related protocols, interfaces, data models, procedures and conventions. Printer manufacturers and vendors of printer related software would benefit from the interoperability provided by voluntary conformance to these standards.

In general, a PWG standard is a specification that is stable, well understood, and is technically competent, has multiple, independent and interoperable implementations with substantial operational experience, and enjoys significant public support.

Contact information:

The Printer Working Group

c/o The IEEE Industry Standards and Technology Organization

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Piscataway, NJ 08854

USA

 

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Members of the PWG and interested parties are encouraged to join the PWG and Character Repertoire WG mailing lists in order to participate in discussions, clarifications and review of the WG product. 

All sections of this document are normative unless noted as informative.

1. Well-known Repertoires

[RS] describes a syntax for referring to a wide range of character repertoires.  In order to promote interoperability, this document designates a small number of repertoires as "well-known".  In this way a print client that only knows the names of the well-known repertoires can get useful results.

The repertoires designated as well-known are:

A conforming printer should support and advertise a well-known repertoire whenever it advertises similar repertoires.  For example, any printer advertising any Cyrillic repertoire should also advertise "unicode_cyrillic".  In this way a client that does not recognize a large number of repertoires can still recognize that some form of Cyrillic printing is possible on this device.

Printers will often support larger repertoires.  If a printer supports a repertoire that is a superset of a well-known repertoire, then it should advertise the well-known repertoire in addition to the superset.  Examples:

2. Printer Operation

A conforming printer should follow these rules:

  1. All printers should support and advertise:
  2. All printers should support the euro (U+20AC) character, even though it is not advertised.
  3. A well-known repertoire should be supported whenever similar ones are, as described above. 
  4. In some document formats (e.g. XHTML-Print) certain additional characters (e.g. as built-in named character entities) are supported for printing, without being advertised in any repertoire.

3. Print Client Operation

Printing protocols (outside of this document) specify how a print client learns about the supported repertoires in a printer.  [RS] describes how to determine which characters are supported in each supported charset.

Once it knows, a client may choose to use this knowledge in any of these ways:

  1. If multiple printers are available, look for one that can print all the characters in a job.
  2. If printing to a printer that can't print all the characters in a job, warn the user.
  3. Make a substitution for a character that won't print.

A. References

[IANA-Charsets]
Available online at http://www.iana.org/assignments/character-sets.
[PWG-SM]
PWG 5105.1-2004 The Printer Working Group Semantic Model, January 20, 2004, P. Zehler. ftp://ftp.pwg.org/pub/pwg/candidates/cs-sm10-20040120-5105.1.pdf, Candidate Standard.
[RFC2119]
"RFC2119 - Key words for use in RFCs to Indicate Requirement Levels", S. Bradner. Available online at http://www.ietf.org/rfc/rfc2119.
[Unicode-Charts]
Unicode code charts, version 4.0.  Beta code charts available online at http://www.unicode.org/charts/u40-beta.html.
[RS]
PWG 5101.2-2004 The Printer Working Group RepertoireSupported Element, February 1, 2004, E. Bradshaw. ftp://ftp.pwg.org/pub/pwg/candidates/cs-crrepsup10-20040201-5101.2.pdf, Candidate Standard.