ISO/IEC 23736-6:2020

INTERNATIONAL ISO/IEC
STANDARD 23736-6
First edition
2020-02
Information technology — Digital
publishing — EPUB 3.0.1 —
Part 6:
Canonical fragment identifiers
Technologies de l'information — Publications numériques — EPUB
3.0.1 —
Partie 6: Identificateurs de fragment canoniques
Reference number
©
ISO/IEC 2020
© ISO/IEC 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO/IEC 2020 – All rights reserved

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
members of ISO or IEC participate in the development of International Standards through technical
committees established by the respective organization to deal with particular fields of technical activity.
ISO and IEC technical committees collaborate in fields of mutual interest. Other international
organizations, governmental and non‐governmental, in liaison with ISO and IEC, also take part in the
work.
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 document should be noted (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.
Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents) or the IEC
list of patent declarations received (see http://patents.iec.ch).
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 the World Wide Web Consortium (W3C) (as EPUB Canonical Fragment
Identifiers 1.1) and drafted in accordance with its editorial rules. It was adopted, under the JTC 1
PAS procedure, by Joint Technical Committee ISO/IEC JTC 1, Information technology.
A list of all parts in the ISO/IEC 23736 series can be found on the ISO websitte.e
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.
© ISO/IEC 2020 – All rights reserved iii

EPUB Canonical Fragment Identifiers 1.1
Recommended Specification 5 January 2017
This version
http://www.idpf.org/epub/linking/cfi/epub-cfi-20170105.html
Latest version
http://www.idpf.org/epub/linking/cfi/epub-cfi.html
Previous version
http://www.idpf.org/epub/linking/cfi/epub-cfi-20161130.html
Previous recommendation
http://www.idpf.org/epub/linking/cfi/epub-cfi-20140628.html
Document history
Changes to this document
Issues addressed in this revision
Report an issue
Errata
Editors
Peter Sorotokin, Adobe
Garth Conboy, Google Inc.
Brady Duga, Google Inc.
John Rivlin, Google Inc.
Don Beaver, Apple Inc.
Kevin Ballard, Apple Inc.
Alastair Fettes, Apple Inc.
Daniel Weck, DAISY Consortium
All rights reserved. This work is protected under Title 17 of the United States Code. Reproduction and
dissemination of this work with changes is prohibited except with the written permission of the International
Digital Publishing Forum (IDPF).
EPUB is a registered trademark of the International Digital Publishing Forum.
Status of this Document
This section describes the status of this document at the time of its publication. Other
documents might supersede this document.
© ISO/IEC 2020 – All rights reserved 1

This document was produced by the EPUB Working Group under the EPUB Working
Group Charter approved on 8 July 2015.
This document has been reviewed by the IDPF membership and is endorsed by the IDPF
Board as a Recommended Specification. This document is considered stable and can be
referenced from other specifications and documents.
Feedback on this document can be provided to the EPUB Working Group's mailing list or
issue tracker.
This document is governed by the IDPF Policies and Procedures.
Table of Contents
1. Overview
1.1. Purpose and Scope
1.2. Terminology
1.3. Typographic Conventions
1.4. Conformance Statements
2. EPUB CFI Definition
2.1. Introduction
2.2. Syntax
2.3. Character Escaping
3. EPUB CFI Processing
3.1. Path Resolution
3.1.1. Step Reference to Child Element or Character Data (/)
3.1.2. XML ID Assertion ([)
3.1.3. Step Indirection (!)
3.1.4. Character Offset (:)
3.1.5. Temporal Offset (~)
3.1.6. Spatial Offset (@)
3.1.7. Temporal-Spatial Offset (~ + @)
3.1.8. Text Location Assertion ([)
3.1.9. Side Bias ([ + ;s=)
3.1.10. Examples
3.2. Sorting Rules
3.3. Intra-Publication CFIs
3.4. Simple Ranges
3.5. Intended Target Location Correction
4. Extending EPUB CFIs
References
› 1 Overview
› 1.1 Purpose and Scope
This section is informative
This specification, EPUB Canonical Fragment Identifier (epubcfi), defines a standardized
method for referencing arbitrary content within an EPUB® Publication through the use of
fragment identifiers.
The Web has proven that the concept of hyperlinking is tremendously powerful, but EPUB
Publications have been denied much of the benefit that hyperlinking makes possible
2 © ISO/IEC 2020 – All rights reserved

because of the lack of a standardized scheme to link into them. Although proprietary
schemes have been developed and implemented for individual Reading Systems, without
a commonly-understood syntax there has been no way to achieve cross-platform
interoperability. The functionality that can see significant benefit from breaking down this
barrier, however, is varied: from reading location maintenance to annotation attachment to
navigation, the ability to point into any Publication opens a whole new dimension not
previously available to developers and Authors.
This specification attempts to rectify this situation by defining an arbitrary structural
reference that can uniquely identify any location, or simple range of locations, in an EPUB
Publication: the EPUB CFI. The following considerations have strongly influenced the
design and scope of this scheme:
The mechanism used to reference content should be interoperable: references to a
reading position created by one Reading System should be usable by another.
Document references to EPUB content should be enabled in the same way that
existing hyperlinks enable references throughout the Web.
Each location in an EPUB file should be able to be identified without the need to
modify the document.
All fragment identifiers that reference the same logical location should be equal
when compared.
Comparison operations, including tests for sorting and comparison, should be able
to be performed without accessing the referenced files.
Simple manipulations should be possible without access to the original files (e.g.,
given a reference deep in a file, it should be possible to generate a reference to the
start of the file).
Identifier resolution should be reasonably efficient (e.g., processing of the first
chapter is not necessary to resolve a fragment identifier that points to the last
chapter).
References should be able to recover their target locations through parser variations
and document revisions.
Expression of simple, contiguous ranges should be supported.
An extensible mechanism to accommodate future reference recovery heuristics
should be provided.
In the case of both Standard EPUB CFIs and Intra-Publication EPUB CFI, this
specification conforms with the guidelines expressed by W3C in Section 6. Best Practices
for Fragid Structures [FragIDBestPractices].
In other words, both standard CFI URIs (e.g., "book.epub#epubcfi(…)", referred media type
"application/epub+zip") and intra-publication CFI URIs (e.g., "package.opf#epubcfi(…)",
referred media type "application/oebps-package+xml") make use of a fragment identifier
syntax that does not overlap with existing schemes in the context of the aforementioned
media types' suffix registrations (i.e., "-xml" and "-zip").
› 1.2 Terminology
© ISO/IEC 2020 – All rights reserved 3

Please refer to [EPUB 3.1] for definitions of EPUB-specific terminology used in this
document.
Standard EPUB CFI
A publication-level EPUB CFI links into an EPUB Publication. The path
preceding the EPUB CFI references the location of the EPUB Publication.
Intra-Publication EPUB CFI
An intra-publication EPUB CFI allows one Content Document to reference
another within the same Rendition of an EPUB Publication. The path preceding
the EPUB CFI references the current Rendition's Package Document.
Refer to Intra-Publication CFIs for more information.
› 1.3 Typographic Conventions
The following typographic conventions are used in this specification:
markup
All markup (elements, attributes, properties), code (JavaScript, pseudo-code),
machine-readable values (string, characters, media types) and file names are in red
monospace font.
markup link
Links to markup and code definitions are in underlined red monospace font.
http://www.idpf.org/
URIs are in navy blue monospace font.
hyperlink
Hyperlinks are underlined and blue.
[reference]
Normative and informative references are enclosed in square brackets.
Term
Terms defined in the Terminology are in capital case.
Term Link
Links to term definitions have a dotted blue underline.
Normative element, attribute and property definitions are in blue boxes.
Informative markup examples are in light gray boxes.
4 © ISO/IEC 2020 – All rights reserved

NOTE
Informative notes are in green boxes with a "Note" header.
CAUTION
Informative cautionary notes are in red boxes with a "Caution" header.
› 1.4 Conformance Statements
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT,
RECOMMENDED, MAY, and OPTIONAL in this document are to be interpreted as described in
[RFC2119].
All sections and appendixes of this specification are normative except where identified by
the informative status label "This section is informative". The application of informative
status to sections and appendixes applies to all child content and subsections they
contain.
All examples in this specification are informative.
› 2 EPUB CFI Definition
› 2.1 Introduction
This section is informative
A fragment identifier is the part of an IRI [RFC3987] that defines a location within a
resource. Syntactically, it is the segment attached to the end of the resource IRI starting
with a hash (#). For HTML documents, IDs and named anchors are used as fragment
identifiers, while for XML documents the Shorthand XPointer [XPTRSH] notation is used
to refer to a given ID.
A Canonical Fragment Identifier (CFI) is a similar construct to these, but expresses a
location within an EPUB Publication. For example:
book.epub#epubcfi(/6/4[chap01ref]!/4[body01]/10[para05]/3:10)
The function-like string immediately following the hash (epubcfi(…)) indicates that this
fragment identifier conforms to the scheme defined by this specification, and the value
contained in the parentheses is the syntax used to reference the location within the
specified EPUB Publication (book.epub). Using the processing rules defined in Path
Resolution, any Reading System can parse this syntax, open the corresponding Content
Document in the EPUB Publication and load the specified location for the user.
A complete definition of the EPUB CFI syntax is provided in the next section.
© ISO/IEC 2020 – All rights reserved 5

NOTE
epub has been prepended to the name of the scheme, as a more generic CFI-like
scheme might be defined in the future for all XML+ZIP-based file formats.
› 2.2 Syntax
(EBNF productions ISO/IEC 14977)
All terminal symbols are in the Unicode Block 'Basic Latin' (U+0000 to U+007F).
fragment = "epubcfi(" , ( path , [ range ] ) , ")" ;
path = step , local_path ;
range = "," , local_path , "," , local_path ;
local_path = { step } , ( redirected_path | [ offset ] );
redirected_path = "!" , ( offset | path );
step = "/" , integer , [ "[" , assertion , "]" ] ;
offset = ( ( ":" , integer ) | ( "@" , number , ":" , number ) | ( "~" , number
, [ "@" , number , ":" , number ] ) ) , [ "[" , assertion , "]" ] ;
number = ( digit-non-zero , { digit } , [ "." , { digit } , digit-non-zero ] ) | (
zero , [ "." , { digit } , digit-non-zero ] ) ;
integer = zero | ( digit-non-zero , { digit } ) ;
assertion = ( ( value , [ "," , value ] ) | ( "," , value ) | ( parameter ) ) {
parameter } ;
parameter = ";" , value-no-space , "=" , csv ;
csv = value , { "," , value } ;
value = string-escaped-special-chars ;
value-no-space = value - ( [ value ] , space , [ value ] ) ;
special-chars = circumflex | square-brackets | parentheses | comma |
semicolon | equal ;
escaped- = ( circumflex , circumflex ) | ( circumflex , square-brackets ) | (
special-chars circumflex , parentheses ) | ( circumflex , comma ) | (
circumflex , semicolon ) | ( circumflex , equal ) ;
character- = ( character - special-chars ) | escaped-special-chars ;
escaped-
special
string-escaped- = character-escaped-special , { character-escaped-special } ;
special-chars
digit = zero | digit-non-zero ;
6 © ISO/IEC 2020 – All rights reserved
...