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This section is non-normative.
This specification defines a file format and processing model for packaging into a single-file container the set of related resources and associated metadata that comprise a digital publication.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at https://www.w3.org/TR/.
This document was published by the Publishing Working Group as a Working Group Note.
GitHub Issues are preferred for discussion of this specification. Alternatively, you can send comments to our mailing list. Please send them to public-publ-wg@w3.org (archives).
Publication as a Working Group Note does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.
This document was produced by a group operating under the W3C Patent Policy.
The group does not expect this document to become a W3C Recommendation.
This document is governed by the 1 March 2019 W3C Process Document.
This section is non-normative.
A digital publication Package is used:
To exchange in-progress packaged publications between different individuals and/or different organizations;
To provide finalized packaged publications from a publisher or conversion house to different distribution or sales channels; and
To deliver packaged publications to users or user agents.
This specification is based on proven technologies and allows digital publications to be packaged in an easy way, hence the term "lightweight" used in its name.
This section is non-normative.
This document uses terminology defined by the W3C Note "Publishing and Linking on the Web" [publishing-linking], including, in particular, user and user agent.
In addition, the following terminology is defined for use in this specification:
Content types that have intrinsic binary format qualities, such as video and audio media types which are already designed for optimum compression, or which provide optimized streaming capabilities.
Content types that benefit from compression due to the nature of their internal data structure, such as file formats based on character strings (for example, HTML, CSS, etc.).
Single-file container for the set of constituent resources and associated metadata that comprise a digital publication.
Preferred starting resource for a digital publication, enabling in some cases the discovery of its Publication Manifest.
Set of constituent resources and associated metadata, organized together in a uniquely identifiable grouping.
[JSON-LD] representation of a digital publication as defined in [pub-manifest].
Base directory of the Package file system.
Only the first instance of a term in a section is linked to its definition.
This section is non-normative.
As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.
The key words MAY, MUST, and SHOULD in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
This section is non-normative.
For packaging the set of constituent resources and associated metadata that comprise a digital publication, this specification uses the ZIP format as specified in ISO/IEC 21320-1:2015 ([ISO21320] and [zip]).
This section is non-normative.
When stored in a Package, resources with Non-Codec content types SHOULD be compressed and the Deflate compression algorithm MUST be used. This practice ensures that file entries stored in the Package have a smaller size.
Resources with Codec content types SHOULD be stored without compression. In such case, compression would introduce unnecessary processing overhead at production time (especially with large resource files) and would impact audio/video playback performance at consumption time.
In some cases, the combination of compression with some encryption schemes might even hinder the ability of user agents to handle partial content requests (e.g. HTTP byte ranges), due to the technical difficulty to determine the length of the full resource ahead of media playback (e.g. HTTP Content-Length header).
This section is non-normative.
A Package MUST include at least one of the following files in its Root Directory:
publication.json,
which MUST be in the format defined for Publication Manifests.index.html which MUST follow the requirements of the
Primary Entry Page of a digital publication.The Root Directory is virtual in nature: a user agent might or might not generate a physical root directory for the contents of the Package if such contents are unpackaged.
The contents of both files MUST not be encrypted.
A Package MUST also include all resources within the bounds of the digital publication, i.e. the finite set of resources obtained from the union of resources listed in the default reading order and resource list of the Publication Manifest.
These resource files MAY be in any location descendant from the Root Directory, or in the Root Directory itself.
Contents within the Package MUST reference these resources via relative-URL strings [url].
The [zip] specification has few constraints on the characters allowed for file and directory names. When crafting such names, authors must be careful to use characters which allow a broad interoperability among operating systems.
This section is non-normative.
If the Package contains a publication.json file
located in the Root Directory,
the Publication Manifest is obtained by opening and parsing this file.
Otherwise, if the Package contains an index.html file
located in the Root Directory,
the Publication Manifest is obtained through the following steps:
document be the result of the extraction of the index.html
file from the Package.text/html or
application/xhtml+xml, terminate this algorithm.link element
in tree order in document whose
rel attribute contains the publication token. null, terminate this algorithm. href attribute's value is the empty string,
terminate this algorithm. If the href attribute value of manifest link has a non-null fragment
identifying an identifier id in document:
script
element in tree order, whose id attribute is equal to
id and whose type attribute is equal to
application/ld+json.null, terminate this
algorithm.This branch is in use when the manifest is embedded in the primary entry page. The
algorithm locates the script element and extract the manifest itself.
href attribute. This branch is in use when the manifest is in a separate file. It performs the standard operations to retrieve the manifest from the Package.
If both index.html and publication.json are present in the Package,
then the Primary Entry Page SHOULD contain a reference to the publication.json file,
following the rules defined in this section.
application/lpf+zip Media TypeThis section is non-normative.
This appendix registers the media type application/lpf+zip
for the Lightweight Packaging Format (LPF).
Lightweight Packaging Format (or LPF) is a container technology based on the [zip] archive format, used for packaging into a single-file container the set of related resources and associated metadata that comprise a digital publication . LPF and its related standards are maintained and defined by the World Wide Web Consortium (W3C).
application
lpf+zip
N/A
N/A
LPF files are binary files in ZIP format.
Security considerations that apply to application/zip also apply to LPF files.
For instance, an archive could contain compressed files that expand
to fill all available disk space on a hard drive.
In consequence, user agents that read LPF files should rigorously check the size
and validity of data retrieved.
In addition, because of the various content types that can be embedded in LPF files,
application/lpf+zip may describe content that poses security issues,
e.g. malicious executable content deliberately included in the package.
However, only in cases where the user agent recognizes and processes the additional content,
or where further processing of that content is dispatched to other user agents,
would security issues potentially arise.
In such cases, matters of security would fall outside the domain of this registration document.
Any format based on LPF, if using content encryption, MUST choose a different MIME media type and file extension than those defined in this specification.
This media type registration is for the Lightweight Packaging Format (LPF),
as described by the Lightweight Packaging Format (LPF) specification located at https://www.w3.org/TR/lpf.
This media type is intended to be used by multiple interoperable applications for the distribution and consumption of ebooks, audiobooks, digital visual narratives and other types of digital publications.
0: PK 0x03 0x04
LPF files are most often identified with the extension
.lpf.
ZIP
None
Ivan Herman (ivan@w3.org)
COMMON
The published specification is a work product of the World Wide Web Consortium (W3C)’s Publishing Working Group. The W3C has change control over this specification.
This section is non-normative.
The editor would like to thank the members of the Publishing Working Group for their contributions to this specification: