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International
Standard
ISO 21720
Second edition
XLIFF (XML Localization
2024-07
Interchange File Format)
XLIFF (Format de fichier XML pour l'échange de données de
localisation)
Reference number
© ISO 2024
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Published in Switzerland
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Foreword
ISO (the International Organization for Standardization) is a worldwide federation of
national standards bodies (ISO member bodies). The work of preparing International
Standards is normally carried out through ISO technical committees. Each member body
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the International Electrotechnical Commission (IEC) on all matters of electrotechnical
standardization.
The procedures used to develop this document and those intended for its further
maintenance are described in the ISO/IEC Directives, Part 1. In particular, the different
approval criteria needed for the different types of ISO document should be noted (see
www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may
involve the use of (a) patent(s). ISO takes no position concerning the evidence, validity or
applicability of any claimed patent rights in respect thereof. As of the date of publication
of this document, ISO had not received notice of (a) patent(s) which may be required to
implement this document. However, implementers are cautioned that this may
not represent the latest information, which may be obtained from the patent database
available at www.iso.org/patents. ISO shall not be held responsible for identifying any or
all such patent rights.
Any trade name used in this document is information given for the convenience of users
and does not constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms
and expressions related to conformity assessment, as well as information about ISO’s
adherence to the World Trade Organization (WTO) principles in the Technical Barriers to
Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by OASIS (as XLIFF Version 2.1, February 2018) and drafted
in accordance with its editorial rules. It was assigned to Technical Committee ISO/TC 37,
Language and terminology, Subcommittee SC 5, Translation, interpreting and related
technology, and adopted under the “fast-track procedure”.
This second edition cancels and replaces the first edition (ISO 21720:2017), which has
been technically revised.
The main changes are as follows (see also Appendix C):
— Two major features are being added in XLIFF Version 2.1:
— Advanced Validation methods;
— Native Support for ITS 2.0.
— The Change Tracking Module was demoted to an extension to free hands of the TC
and other implementers while working on a new version of the Change Tracking
Module for XLIFF 2.2.
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— A major bug fix was performed on the core xsd. The core xsd now enforces the
xs:language data type on the srcLang and trgLang attributes. It was critical to make
this fix, because -- as per OASIS policy -- validation artifacts would prevail over the
prose provisions that are correct in both XLIFF 2.1 and XLIFF 2.0.
— Also an erroneously omitted Constraint of the xml:lang attribute on the
element has been added/restored in the normative text.
— Apart from the five (5) major changes mentioned above, numerous editorial bugfixes
were made to secure greater clarity, either by fixing example errors or omissions, or
by reorganizing normative content, so that the intent becomes clear and unequivocal
at some troublesome places highlighted by XLIFF 2.0 implementers.
— Importantly, the TC decided to drop informative listings of the validation artifacts
that had bloated the spec extent unnecessarily, were hard to keep in sync with the
actual normative artifacts, while their actual usability proved rather limited --
readers who were able to read schema languages would not actually read them as
printed listings and would anyways refer to the actual validation artifacts that are
now referenced more prominently.
Any feedback or questions on this document should be directed to the user’s
national standards body. A complete listing of these bodies can be found at
www.iso.org/members.html.
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Table of Contents
1 Introduction
1.0 IPR Policy
1.1 Terminology
1.1.1 Key words
1.1.2 Definitions
1.1.3 Key concepts
1.2 Normative References
1.3 Non-Normative References
2 Conformance
3 Fragment Identification
3.1 Selectors for Core Elements
3.2 Selectors for Modules and Extensions
3.3 Relative References
3.4 Examples
4 The Core Specification
4.1 General Processing Requirements
4.2 Elements
4.2.1 Tree Structure
4.2.2 Structural Elements
4.2.3 Inline Elements
4.3 Attributes
4.3.1 XLIFF Attributes
4.3.2 XML namespace
4.4 CDATA sections
4.5 XML Comments
4.6 XML Processing Instructions
4.7 Inline Content
4.7.1 Text
4.7.2 Inline Codes
4.7.3 Annotations
4.7.4 Sub-Flows
4.7.5 White Spaces
4.7.6 Bidirectional Text
4.7.7 Target Content Modification
4.7.8 Content Comparison
4.8 Segmentation
4.8.1 Segments Representation
4.8.2 Segments Order
4.8.3 Segmentation Modification
4.8.4 Best Practice for Mergers (Informative)
4.9 Extension Mechanisms
4.9.1 Extension Points
4.9.2 Constraints
4.9.3 Processing Requirements
5 The Modules Specifications
5.1 Translation Candidates Module
5.1.1 Introduction
5.1.2 Module Namespace and Validation Artifacts
5.1.3 Module Fragment Identification Prefix
5.1.4 XLIFF Core Reuse
5.1.5 Translation Candidate Annotation
5.1.6 Module Elements
5.1.7 Module Attributes
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5.1.8 Example
5.2 Glossary Module
5.2.1 Introduction
5.2.2 Module Namespace and Validation Artifacts
5.2.3 Module Fragment Identification Prefix
5.2.4 Module Elements
5.2.5 Module Attributes
5.2.6 Example
5.3 Format Style Module
5.3.1 Introduction
5.3.2 Module Namespace and Validation Artifacts
5.3.3 Module Fragment Identification Prefix
5.3.4 Module Specification
5.3.5 Module Attributes
5.4 Metadata Module
5.4.1 Introduction
5.4.2 Module Namespace and Validation Artifacts
5.4.3 Module Fragment Identification Prefix
5.4.4 Module Elements
5.4.5 Module Attributes
5.5 Resource Data Module
5.5.1 Introduction
5.5.2 Module Namespace and Validation Artifacts
5.5.3 Module Fragment Identification Prefix
5.5.4 Module Elements
5.5.5 Module Attributes
5.5.6 Examples
5.6 Change Tracking Extension (Informative)
5.6.1 Introduction
5.6.2 Module Namespace and Validation Artifacts
5.6.3 Module Fragment Identification Prefix
5.6.4 Module Elements
5.6.5 Module Attributes
5.6.6 Example
5.7 Size and Length Restriction Module
5.7.1 Introduction
5.7.2 Module Namespace and Validation Artifacts
5.7.3 Module Fragment Identification Prefix
5.7.4 Module Elements
5.7.5 Module Attributes
5.7.6 Standard profiles
5.7.7 Third party profiles
5.7.8 Conformance
5.7.9 Example
5.8 Validation Module
5.8.1 Introduction
5.8.2 Module Namespace and Validation Artifacts
5.8.3 Module Fragment Identification Prefix
5.8.4 Module Elements
5.8.5 Module Attributes
5.9 ITS Module
5.9.1 Introduction
5.9.2 Module Namespace and Validation Artifacts
5.9.3 Module Fragment Identification Prefix
5.9.4 Conformance to the ITS Module Specification
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5.9.5 ITS Tools Referencing
5.9.6 ITS data categories defined in the ITS Module
5.9.7 ITS data categories that have a partial overlap with XLIFF features
5.9.8 ITS data categories available through XLIFF Core and other Modules
5.9.9 ITS data categories not represented in XLIFF
5.9.10 ITS Mapping Annotations
5.9.11 Module Elements
5.9.12 Module Attributes
5.9.13 Example file
Appendixes
A Media Type Registration Template for XLIFF Version 2.0 and higher Versions
A.1 Registration Template
A.1.1 Detailed Security Considerations
A.1.1.1 Privacy, trust and integrity
A.1.1.2 Core
A.1.1.3 Resource Data Module
A.1.1.4 ITS Module
A.1.1.5 Other potentially security sensitive constructs
B Machine Readable Validation Artifacts (Informative)
B.1 XML Schemas Tree
B.2 Support Schemas
C Specification Change Tracking (Informative)
C.1 High Level Summary of Changes made in Comparison to XLIFF Version
2.0
C.2 Tracking of changes made in response to Public Reviews
C.2.1 Tracking of changes in response to the Public Review of the Candidate
OASIS Standard 01
C.2.2 Tracking of changes in response to the 4th Public Review
C.2.3 Tracking of changes in response to the 3rd Public Review
C.2.4 Tracking of changes in response to the 2nd Public Review
C.2.5 Tracking of changes in response to the 1st Public Review
D Acknowledgements (Informative)
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International Standard ISO 21720:2024(en)
1 Introduction
XLIFF is the XML Localization Interchange File Format designed by a group of
multilingual content publishers, software providers, localization service providers,
localization tools providers, and researchers. It is intended to give any multilingual
content owner a single interchange file format that can be understood by any
localization provider, using any conformant localization tool. While the primary focus
is on being a lossless interchange format, usage of XLIFF as a processing format is
neither encouraged nor discouraged or prohibited.
All text is normative unless otherwise labeled. The following common methods are
used for labeling portions of this specification as informative and hence non-
normative:
Appendices and sections marked as "(Informative)" or "Non-Normative" in title,
Notes (sections with the "Note" title),
Warnings (sections with the "Warning" title),
Examples (mainly example code listings, tree diagrams, but also any inline examples or
illustrative exemplary lists in otherwise normative text),
Schema and other validation artifacts listings (the corresponding artifacts are normative, not
their listings).
1.0 IPR Policy
This specification is provided under the RF on RAND Terms Mode of the OASIS IPR
Policy, the mode chosen when the Technical Committee was established. For
information on whether any patents have been disclosed that may be essential to
implementing this specification, and any offers of patent licensing terms, please refer
to the Intellectual Property Rights section of the Technical Committee web page
(https://www.oasis-open.org/committees/xliff/ipr.php).
1.1 Terminology
1.1.1 Key words
The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL are to be interpreted as
described in [RFC 2119].
1.1.2 Definitions
Agent
any application or tool that generates (creates), reads, edits, writes,
processes, stores, renders or otherwise handles XLIFF Documents.
Agent is the most general application conformance target that subsumes all
other specialized user agents disregarding whether they are defined in this
specification or not.
Enrich, Enriching
the process of associating module and extension based metadata and
resources with the Extracted XLIFF payload
Processing Requirements
• Enriching MAY happen at the time of Extraction.
Note
Extractor knowledge of the native format is not assumed while
Enriching.
Enricher, Enricher Agent
any Agent that performs the Enriching process
Extract, Extraction
the process of encoding localizable content from a native content or User
Interface format as XLIFF payload, so that localizable parts of the content in
the source language are available for Translation into the target language
along with the necessary context information
Extractor, Extractor Agent
any Agent that performs the Extraction process
Merge, Merging
the process of importing XLIFF payload back to the originating native format,
based on the full knowledge of the Extraction mechanism, so that the
localized content or User Interface strings replace the source language in the
native format
Merger, Merger Agent
an Agent that performs the Merge process
Warning
Unless specified otherwise, any Merger is deemed to have the
same knowledge of the native format as the Extractor
throughout the specification.
Mergers independent of Extractors can succeed, but it is out of
scope of this specification to specify interoperability for
Merging back without the full Extractor knowledge of the native
format.
Modify, Modification
the process of changing core and module XLIFF structural and inline
elements that were previously created by other Writers
Processing Requirements
• XLIFF elements MAY be Modified and Enriched at the same time.
Note
Extractor or Enricher knowledge of the native format is not
assumed while Modifying.
Modifier, Modifier Agent
an Agent that performs the Modification process
Translation, Translate
a rendering of the meaning of the source text, expressed in the target
language
Writer, Writer Agent
an Agent that creates, generates, or otherwise writes an XLIFF Document for
whatever purpose, including but not limited to Extractor, Modifier, and
Enricher Agents.
Note
Since XLIFF is intended as an exchange format rather than a
processing format, many applications will need to generate
XLIFF Documents from their
...