Working Group Draft 20120222
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Status of this Document
This is an IDPF Working Group draft that has no official status at this time. It may be updated, replaced, or rendered obsolete by other documents at any time. Its publication does not imply endorsement by the IDPF membership or the IDPF EPUB 3 Working Group.
Table of Contents
EPUB documents, unlike print books or PDF files, are designed to change. The content flows, or reflows, to fit the screen and to fit the needs of the reader. The EPUB 3.0 Specification says that “content presentation should adapt to the user rather than the user having to adapt to a particular representation of content.”
But this principle doesn’t work for all types of documents. Sometimes content and design are so intertwined they cannot be separated. Any change in appearance risks changing the meaning, or losing all meaning. Fixed-layout documents give content creators greater control over presentation, when a reflowable EPUB is not suitable for the content.
This document, EPUB 3 Fixed-Layout Documents, defines a set of metadata properties to allow declarative expression of intended rendering behaviors of fixed-layout documents in the context of EPUB 3.
EPUB 3 affords three mechanisms for representing fixed-layout content in EPUB 3 documents: as bitmap images, as SVG, and as XHTML that uses CSS absolute positioning. When fixed-layout content is necessary, the author's choice between these representations will depend on many factors including desired degree of precision, file size, accessibility, etc. This document does not attempt to dictate this choice, and a fully-conforming EPUB 3 Reading System should support all three of these options.
| Name |
|
|---|---|
| Description |
Specifies whether the given Publication or spine item is reflowable or pre-paginated. |
| Value |
|
| Usage |
Package Document Package Document |
| Initial |
In In |
| Cardinality |
In In |
When the rendition:layout property is specified on the Package
Document meta element, it indicates that the paginated or
reflowable rendering style (see below) applies globally for the given
Publication (i.e. for all spine items).
As ‘reflowable’ is the initial value of this property in the
meta usage context, this value must be assumed by Reading
Systems as the global value if no meta element carrying this
property occurs in the Package Document instance.
The rendition:layout property may also be specified on the
Package Document spine itemref element, and will in this case
override the global value for the
given spine item. (Refer to Specifying name-value
pairs on the spine itemref element for syntactical rules specific to
local specification.)
For any given spine item that has attained a value for the
rendition:layout property either through inheritance from
a global specification or through a local specification, the allowed
values have the following meaning:
It is common behavior for Reading Systems to restrict or deny the application of User or User Agent stylesheets to pre-paginated documents, since as a result of intrinsic properties of such documents, dynamic style changes are highly likely to have unintended consequences. Authors should take the negative impact on usability and accessibility that these restrictions have into account when choosing to use pre-paginated instead of reflowable content.
| Name |
|
|---|---|
| Description |
Specifies which orientation(s) the Author intends for the given Publication or spine item to be rendered in. |
| Value |
|
| Usage |
Package Document Package Document |
| Initial |
In In |
| Cardinality |
In In |
When the rendition:orientation property is specified on the
Package Document meta element, it indicates that the intended
orientation applies globally for the given Publication (i.e. for all spine
items).
As ‘auto’ is the initial value of this property in the meta
usage context, this value must be assumed by Reading Systems as the global
value if no meta element carrying this property occurs in the
Package Document instance.
The rendition:orientation property may also be specified on
the Package Document spine itemref element, and will in this
case override the global value
for the given spine item. (Refer to Specifying
name-value pairs on the spine itemref element for syntactical
rules.)
For any given spine item that has attained a value for the
rendition:orientation property either through inheritance
from a global specification or
through a local specification, the
allowed values have the following meaning:
Reading Systems that support multiple orientations should, unless the given value is 'auto', convey the intended orientation to the user. The means by which the intent is conveyed is implementation specific.
| Name |
|
|---|---|
| Description |
Specifies the intended Reading System synthetic spread behavior for this Publication or spine item. |
| Value |
|
| Usage |
Package Document Package Document |
| Initial |
In In |
| Cardinality |
In In |
When the rendition:spread property is specified on the Package
Document meta element, it indicates that the intended synthetic
spread behavior applies globally for the given Publication (i.e. for all
spine items).
As ‘auto’ is the initial value of this property in the meta
usage context, this value must be assumed by Reading Systems as the global
value if no meta element carrying this property is occurs in
the Package Document instance.
The rendition:spread property may also be specified on the
Package Document spine itemref element, and will in this case
override the global value for the
given spine item. (Refer to Specifying name-value
pairs on the spine itemref element for syntactical rules.)
For any given spine item that has attained a value
for the rendition:spread property either through inheritance
from a global specification or through
a local specification, the allowed
values have the following meaning, where synthetic spread is
defined as the rendering of two adjacent pages simultaneously on the
device screen.
When synthetic spreads are used, the size given via viewport/viewbox metadata represents the size of one page in the spread.
Refer to 3.4.12 The spine Element for information about declaration of
global flow directionality using the
page-progression-direction attribute and that of local
page-progression-direction within content documents.
Refer also
to Issue 205 for discussions on forthcoming specifications of
precedence rules for the page-progression-direction
attribute and the writing-mode and direction
properties within XHTML Content Documents.
| Names |
and, as defined in [Publications30]
|
|---|---|
| Description |
Specifies the forced placement of a Content Document in a synthetic spread |
| Usage |
Package Document spine |
| Cardinality |
Zero or one |
When a Reading System is rendering synthetic spreads, the default behavior is to populate the spread, which conceptually consists of two adjacent viewports, by rendering the next Content Document in the next available unpopulated viewport, where the location of “next” is determined by the given page progression direction, or by local declarations within content documents. By providing one of the page-spread-* properties on the spine itemref element, the author can override this automatic population behavior by forcing the given Content Document to be placed in a particular viewport.
The page-spread-left and page-spread-right
properties are defined in [Publications30].
This document defines one additional property,
rendition:page-spread-center, which indicates that the
synthetic spread mode should be overridden such that instead of two adjacent
viewports, a single viewport must be used, and positioned at the center of the
screen. Note that the presence of rendition:page-spread-center
does not in itself affect the viewport dimensions.
The page-spread-left , page-spread-right and
rendition:page-spread-center properties apply to both
pre-paginated and reflowable content, and they only apply when the Reading
System is creating synthetic spreads.
When the metadata properties defined in this document are included in an EPUB 3
Package Document, they must be mapped to the URI
http://www.idpf.org/vocab/rendition/# using the
prefix attribute, as defined in EPUB Publications 3.0 vocabulary association .
<package … prefix="rendition: http://www.idpf.org/vocab/rendition/#">
…
</package>
Implementors should note that future revisions of [Publications30] may establish the vocabulary represented by the URI
http://www.idpf.org/vocab/rendition/# as a reserved vocabulary. In this case, the result will be that a) explicit
mapping declaration using the prefix attribute will no longer be
applicable, and b) the prefix ‘rendition’ will be reserved for this vocabulary.
Future revisions of [Publications30] may also
integrate the properties defined here into the Package Document default
vocabulary. In this case the properties defined herein will be allowed to occur
in Package Documents without a prefix.
Note that Package Documents may include additional proprietary metadata properties that pertain to layout expressions (refer to Vocabulary Association Mechanisms for further information on extensibility ). Reading Systems must ignore such expressions if they behaviorally conflict with the property semantics defined in this document.
In the context of the properties defined in this document, and when specifying
property name-value pairs in the properties attribute on the
Package Document spine itemref element, the following syntax must
be used.
The property name and value is concatenated into a single string using a
hyphen-minus character (U+002D) as separator. Note
that leading and trailing whitespace around the separator character is not
allowed.
For example, to express that the rendition:layout property has the
value ‘reflowable’ for the given spine item, the string
‘rendition:layout-reflowable’ is used:
<itemref … properties="rendition:layout-reflowable"/>
This section defines how to express intrinsic dimensionality properties of XHTML and
SVG Content Documents [ContentDocs30]. Each spine
item which has the ‘pre-paginated’ value set for its rendition:layout
property must contain the viewport (for XHTML) or viewBox (for SVG) rendering
instructions as defined below.
For both XHTML and SVG Content Documents, the dimension (viewport/viewbox) expressions identified below define the CSS initial containing block expressed in CSS Pixels. [CSS]
Reading Systems must clip XHTML content to the initial containing block dimensions declared in the viewport meta tag/viewBox attribute, and therefore content positioned outside of the initial containing block is not going to be visible. When the initial containing block aspect ratio does not match the aspect ratio of the Reading System content display area, Reading Systems may position the initial containing block inside the area to accommodate the user interface; in other words, added letter-boxing space may appear on either side (or both) of the content.
This document does not define how the initial containing block will be placed within the Reading System content display area.
XHTML viewport dimensions are expressed using the viewport meta tag using syntax as per [MetaTags]. In this version of this document, only the width and height expressions are required to be recognized by Reading Systems.
Example:
<head>
…
<meta name="viewport" content="width=1200, height=600"/>
…
</head>
SVG viewport dimensions are defined using the viewBox attribute [SVG11].
Example:
<svg xmlns="http://www.w3.org/2000/svg"
version="1.1" width="100%" height="100%"
viewBox="0 0 844 1200">
…
</svg>
Fully fixed-layout content, intended to be rendered using synthetic spreads in landscape orientation, and no spreads in portrait orientation.
OPF
<meta property="rendition:layout">pre-paginated</meta> <meta property="rendition:spread">landscape</meta>
XHTML
All content documents contain:
<meta name="viewport" content="width=512, height=600"/>
Note: to leave the spread behavior up to the Reading System, the rendition:spread element is either omitted or set to ‘auto’.
Fully fixed-layout content, intended to be rendered without synthetic spreads, and locked to landscape orientation.
OPF
<meta property="rendition:layout">pre-paginated</meta> <meta property="rendition:spread">none</meta> <meta property="rendition:orientation">landscape</meta>
XHTML
All content documents contain:
<meta name="viewport" content="width=1024, height=600"/>
Reflowable content with a single fixed-layout page (title page), where the fixed-layout page is intended for right-hand spread slot if the device renders synthetic spreads.
OPF
<meta property="rendition:layout">reflowable</meta> <meta property="rendition:spread">auto</meta> … <itemref id="titlepage" properties="page-spread-right rendition:layout-pre-paginated"/>
XHTML
The content document representing the title page contains:
<meta name="viewport" content="width=684, height=1024"/>
Note that in this example, both the rendition:layout and
rendition:spread properties are set to their initial values,
which means that these two meta elements can be omitted without any impact on
the resulting expression.
Fully fixed-layout content where synthetic spreads - if used - must be disabled for a center plate.
OPF
<meta property="rendition:layout">pre-paginated</meta> <meta property="rendition:spread">auto</meta> … <itemref id="center-plate" properties="rendition:page-spread-center"/>
XHTML
The content document representing the center plate contains:
<meta name="viewport" content="width=1024, height=600"/>
Note that even though the center plate viewport dimension expression indicates landscape orientation, the author has omitted the orientation property, leaving it to the Reading System to decide how to handle the situation. Note also that the rendition:spread=none expression is not needed here, as the rendition:page-spread-center property already specifies semantics that dictates that synthetic spreads be disabled.
Note finally that in this example, the rendition:spread property is
set to its initial value, and so it can be omitted without any impact on the
resulting expression.
Reflowable content with a fixed-layout two-page center plate that is intended to be rendered using synthetic spreads in any device orientation. The author has left spread behavior for the other (reflowable) parts of the publication undefined, since the global value of rendition:spread is initialized to ‘auto’.
OPF
<spine page-progression-direction=”ltr”>
…
<itemref id="center-plate-left" properties="rendition:spread-both page-spread-left"/>
<itemref id="center-plate-right" properties="rendition:spread-both page-spread-right"/>
…
</spine>
XHTML
The two content documents representing the center plate contains:
<meta name="viewport" content="width=512, height=600"/>
Fully fixed-layout content which includes three separate stylesheets used for three different device categories, using [MediaQueries].
OPF
<meta property="rendition:layout">pre-paginated</meta>
XHTML
<link rel="stylesheet" href="eink-style.css" media="(max-monochrome: 3)"/>
<link rel="stylesheet" href="skinnytablet-style.css" media="((color) and
(max-height:600px) and (orientation:landscape), (color) and (max-width:600px)
and (orientation:portrait))" />
<link rel="stylesheet" href="fattablet-style.css" media="((color) and
(min-height:601px) and (orientation:landscape), (color) and (min-width:601px)
and (orientation:portrait)" />
The tables below describe how the vocabulary defined in this document maps to some of the pre-existing proprietary metadata vocabularies for fixed-layout expressions.
| Amazon Property | IDPF Equivalent (prefixes omitted for clarity) |
|---|---|
|
fixed-layout (true | false) |
layout (reflowable | pre-paginated) |
|
original-resolution (width, ‘x’, height) |
viewport (XHTML meta) |
|
orientation (portrait | landscape) |
orientation (portrait | landscape | auto) |
|
book-type (children | comic) |
not applicable |
|
RegionMagnification (true | false) |
not applicable, proprietary |
| Sony Property | IDPF Equivalent (prefixes omitted for clarity) |
|---|---|
|
fixed-layout (true | false) |
layout (reflowable | pre-paginated) |
|
orientation (portrait | landscape | auto) |
orientation (portrait | landscape | auto) |
|
page-spread (full | double | auto) |
rendition:spread (none | portrait | landscape | both | auto) |
|
overflow-scroll (true | false) |
defined in CSS |
|
viewport |
viewport (XHTML meta) |
Note that for page-spread, the values for 'portrait' and 'both' would
all map to 'double', 'landscape' would map to 'auto', and 'none' would map to
'full'.
Apple currently stores some of this metadata in an XML file in META-INF.
| Apple Property | IDPF Equivalent (prefixes omitted for clarity) |
|---|---|
|
fixed-layout (true | false) |
layout (reflowable | pre-paginated) |
|
viewport (XHTML meta) |
viewport (XHTML meta) |
|
orientation (landscape-only | portrait-only | none) |
orientation (landscape | portrait | auto) |
|
platform name |
no equivalent |
|
open-to-spread (true | false) |
no equivalent |
An informative note at the end of Section 3.3.1 ("CSS 2.1") of EPUB 3 Content Documents has been a source of some confusion relative to fixed layout and EPUB 3. This appendix intends to clarify that note until the concerned specification is updated accordingly.
The note states: "The ability of Reading Systems to paginate absolutely positioned layouts is not guaranteed, so reliance on absolute positioning is discouraged. Reading Systems might not support these property values.".
First, given its location in the CSS section of the specification, it should be noted that this statement is only applicable to fixed-layout documents that utilize CSS. Second, this note does not imply that the "absolute" value of the position property is not in the EPUB 3 CSS profile; "position:absolute" is in fact part of the profile, since it is part of its baseline (CSS 2.1). Only the "fixed" value is excluded from the EPUB 3 CSS Profile (as stated in normative prose above the note).
Lastly, this note does not discourage use of CSS for absolutely positioned layouts but only reliance on such for content expected to be delivered to arbitrary Reading Systems, which as stated may not support these values. In particular, EPUB 2.x Reading Systems will likely not support these values, as they were not included in the EPUB 2 CSS Profile. Many uses of absolutely-positioned CSS will gracefully degrade if these property values are ignored, and such graceful degradation behavior (non-reliance) is encouraged.
[ContentDocs30]EPUB Content Documents 3.0
[CSS]Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification
[MediaQueries]Media Queries
[MetaTags]Supported Meta Tags (informative)
[Publications30]EPUB Publications 3.0