The guide element [OPF2] is a legacy feature that previously provided machine-processable navigation to keystructures in an EPUB Publication. It is replaced in EPUB 3 by landmarks in the EPUB Navigation Document.
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Authors are advised to use the value "both" instead, as spreads thatare readable in portrait orientation are also readable in landscape. ReadingSystems SHOULD treat the value "portrait" as a synonym of"both" and create spreads regardless of orientation.
The epub:typeattribute [ContentDocs32] is REQUIRED on a element descendants ofthe landmarksnav element. The structural semantics of each link target within thelandmarksnav element is determined by the value of this attribute.
EPUB Navigation Documents MAY include one or more nav elements in addition tothe toc, page-list and landmarksnav elements defined in the preceding sections. These additionalnav elements SHOULD have an epub:type attribute to provide amachine-readable semantic, and MUST have a human-readable heading as their first child.
A ZIP-based archive with the file extension .epub bundles the EPUB publication'sresources for distribution. As conformant ZIP archives, EPUB publications can be unzipped by manysoftware programs, simplifying both their production and consumption.
While conceptually simple, an EPUB publication is more than just a collection of HTML pages anddependent assets in a ZIP package as presented here. Additional information about the primaryfeatures and functionality that EPUB publications provide to enhance the reading experience isavailable from the referenced specifications, and a more general introduction to the features ofEPUB 3 is provided in the non-normative [[epub-overview-33]].
Refer to [[epub-rs-33]] for the processing requirements for reading systems. Although it is notnecessary that [=EPUB creators=] read that document to create EPUB publications, an understanding ofhow reading systems present the content can help craft publications for optimal presentation tousers.
Inclusion as a core media type resource does not mean that all reading systems will support therendering of a resource. Reading system support also depends on the capabilities of theapplication (e.g., a reading system with a [=viewport=] must support image core media typeresources, but a reading system without a viewport does not). Refer to Core media types [[epub-rs-33]] for moreinformation about which reading systems rendering capabilities require support for which coremedia type resources.
For example, URLs like :12345/ or :12345/ honor these properties. But URLs like :12345/path/to.epub/,file:///path/to.epub#path=/, or jar:file:/path/to.epub!/EPUB/do not (parsing the URL string ".." with these three examples as base wouldreturn :12345/path/, file:///path/, and a parsingerror, respectively). It is the responsibility of the reading system to assign a URL to theroot directory that complies with the properties defined above.
Although the EPUB container provides the ability to reference more than onepackage document, this specification does not define how to interpret, or selectfrom, the available options. Refer to [[epub-multi-rend-11]] for moreinformation on how to bundle more than one rendering of the content.
[=EPUB creators=] should use unprefixed properties and [=reading systems=] should supportcurrent CSS specifications. This specification retains the widely used prefixedproperties from [[epubcontentdocs-301]] but removes support for the less-used ones. EPUBcreators should use CSS-native solutions for the removed properties wheneveravailable.
[=EPUB creators=] should note that supportfor container-constrained scripting in reading systems is only recommended inreflowable documents [[epub-rs-33]]. Furthermore, [=reading system=] support in[=fixed-layout documents=] is optional.
[=EPUB creators=] should note that support for spine-level scripting in [=readingsystems=] is only recommended in fixed-layout documentsand reflowable documents set toscroll [[epub-rs-33]]. Furthermore, reading system support in all other contextsis optional.
The EPUB navigation document is a special type of [=XHTML content document=] that defines the table of contents for [=reading systems=]. It may also include otherspecialized navigation elements, such as a page list and a list ofkey landmarks. These navigation elements have additional restrictions on their content to facilitate theirprocessing.
The landmarks nav element identifies fundamental structural components in thecontent to enable [=reading systems=] to provide the user efficient access to them (e.g.,through a dedicated button in the user interface).
The [^/epub:type^] attribute is REQUIRED on a element descendants of thelandmarks nav element. The structural semantics of each link target within thelandmarks nav element is determined by the value of this attribute.
[=EPUB creators=] should limit the number of items they define in the landmarks navto only items that a reading system is likely to use in its user interface. The element is notmeant to repeat the table of contents.
Although the landmarks nav is intended for reading system use, EPUB creators shouldstill ensure that the labels for the landmarks nav are human readable. Readingsystems may expose the links directly to users.
[=EPUB navigation documents=] MAY contain one or more nav elements in addition tothe toc, page-list, and landmarks nav elements defined inthe preceding sections. If these nav elements are intended for [=reading system=]processing, they MUST have an [^/epub:type^] attribute and are subject to the content modelrestrictions defined in .
Although it is possible to reuse the [=EPUB navigation document=] in the [=EPUB spine spine=], itis often the case that not all of the navigation structures, or branches within them, are needed.[=EPUB creators=] will often want to hide the page list and landmarks navigation elements or trim the branches of the table ofcontents for books that have many levels of subsections.
[=EPUB publications=], unlike print books or PDF files, are designed to change. The contentflows, or reflows, to fit the screen and to fit the needs of the user. As noted in Rendering and CSS "content presentationadapts to the user, rather than the user having to adapt to a particular presentation ofcontent." [[epub-overview-33]]
Two rows of schematic views of tablets (three in each row). The tablets in the toprow are in portrait mode, and in landscape mode in the bottom one. The schematicviews of the tablets within a row are linked with left-to-right arrows.
Two rows of schematic views of tablets (three in top row, and two in the bottom). Thetablets in the top row are in portrait mode, and in landscape mode in the bottomone. The schematic views of the tablets within a row are linked with left-to-rightarrows.
Two rows of schematic views of tablets (two in each row). The tablets in the top roware in portrait mode, and in landscape mode in the bottom one. The schematic viewsof the tablets within a row are linked with left-to-right arrows.
The seq element MUST contain an epub:textref attribute. As seq elements do notprovide synchronization instructions, this attribute allows a [=reading system=] to matchthe fragment to a location in the text.
Both the epub:textref attribute and the [^text^] element's srcattribute may contain a [=URL-fragment string=] that references a specific part (e.g., anelement via its ID) of the associated [=EPUB content document=].
The granularity level of the media overlay depends on how [=EPUB creators=] mark up the[=EPUB content document=] and the type of fragment identifier they use in the [^text^]elements' src attributes and the [^seq^] elements' epub:textrefattrbutes. For example, when referencing [[html]] elements, if the finest level of markup isat the paragraph level, then that is the finest possible level for media overlaysynchronization. Likewise, if sub-paragraph markup is available, such as [[html]] [^span^]element representing phrases or sentences, then finer granularity is possible in the mediaoverlay. Finer granularity gives users more precise results for synchronized playback whennavigating by word or phrase and when searching the text but increases the file size of the[=media overlay documents=]. Fragment identifier schemes that do not rely on the presence ofelements could provide even finer granularity, where supported.
The epub:type attribute facilitates [=reading system=] behavior appropriate for thesemantic type(s) indicated. Examples of these behaviors are skippability and escapability and table reading mode [[?epub-rs-33]].
While reading, users may want to turn on or off certain features of the content, such asfootnotes, page numbers, or other types of secondary content. This feature is calledskippability. [=Reading systems=] use the semantic information provided by media overlayelements' epub:type attribute todetermine when to offer users the option of skippable features.
This list is non-exhaustive list, however. It represents terms from the Structural SemanticsVocabulary [[?epub-ssv-11]] for which [=reading systems=] are most likely to offer theoption of escapability.
As the [=EPUB navigation document=] is an [=XHTML content document=], [=EPUB creators=] may associatea [=media overlay document=] with it. Unlike traditional XHTML content documents, however, [=readingsystems=] must present the EPUB navigation document to users even when it is not included in the[=EPUB spine spine=] (see Navigation document processing[[epub-rs-33]]). As a result, the method in which an associated media overlay behaves can changedepending on the context:
As the current WCAG guidelines (version 2) are heavily focused on web pages, a separate specification, EPUB Accessibility [[epub-a11y-11]], defines how to apply the standardto EPUB publications. It also adds EPUB-specific requirements and recommendations for metadata,pagination, and media overlays.
This specification recommends that EPUB publications conform to the accessibilityrequirements defined in [[epub-a11y-11]]. A benefit of following this recommendation isthat it helps to ensure that EPUB publications meet the accessibility requirements legislated injurisdictions around the world. 2ff7e9595c
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