@chunk attributeThe specification defines tokens for the @chunk attribute that cover
the most common chunking scenarios. These tokens can be used to
override whatever default chunking behavior is set by a processor. Chunking is necessarily
format specific, with chunked output required for some and not supported for other rendered
formats. Chunking is also implementation specific with some implementations supporting some,
but not all, chunking methods, or adding new methods to the standard ones described in this
specification.
The value of the @chunk attribute consists of one or
more space delimited tokens. Tokens are defined in three categories: for selecting
topics, for setting chunking policies, and for defining how the chunk values impact
rendering. It is an error to use two tokens from the same category on a single
<topicref> element.
select-topic: Selects an individual topic without
any ancestors, descendents, or peers from within the same document.select-document: Selects all topics in the target
document.select-branch: Selects the target topic together
with its descendent topics.<map> element, the policy becomes the default policy
for all topic references. When specified on a topic reference, the policy applies
only to that <topicref> and not to any descendant
<topicref> elements.by-topic: A separate output chunk is produced for
each of the selected topics. In particular, topics that are part of
multi-topic documents are processed as though they are the root topics
within a separate XML document.by-document: A single output chunk is produced for
the referenced topic or topics, as though the selected topics were all
children of the same document.to-content: The selection should be rendered as a
new chunk of content. <topicref>, this means
that the topics selected by this <topicref> and
its children will be rendered as a single chunk of content.<map> element, this
indicates that the contents of all topics referenced by the map are to
be rendered as a single document.<topicref> that contains a
title but no target, this indicates that processors MUST generate a title-only topic in
the rendered result, along with any topics referenced by child
<topicref> elements of this
<topicref>. The rendition address of the
generated topic is determined as defined for the
@copy-to attribute. If the @copy-to
attribute is not specified and the <topicref>
has no @id attribute, the address of the generated
topic is not required to be predictable or consistent across rendition
instances.For cross references to <topicref> elements,
if the value of the @chunk attribute is "to-content" or
is unspecified, the cross reference is treated as a reference to the
target topic. If the reference is to a <topicref>
with no target, it is treated as a reference to the generated title-only
topic.
to-navigation
(DEPRECATED): The "to-navigation" token is deprecated in DITA 1.3. In earlier
releases, the "to-navigation" token indicates that a new chunk of navigation
should be used to render the current selection (such as an individual Table
of Contents or related links). When specified on the
<map> element, this token indicates that the map
should be presented as a single navigation chunk. If a cross reference is
made to a <topicref> that has a title but no target,
and the @chunk value of that
<topicref> is set to "to-navigation", the
resulting cross reference is treated as a reference to the rendered
navigation document (such as an entry in the table of contents).Some tokens or combinations of tokens might not be appropriate for all output types. When unsupported or conflicting tokens are encountered during output processing, processors SHOULD produce warning or error messages. Recovery from such conflicts or other errors is implementation dependent.
There
is no default value for the @chunk attribute on most elements and the
@chunk attribute does not cascade from container elements, meaning
that the @chunk value on one <topicref> is not
passed to its children. A default by-xxx policy for an entire map can be established by setting the @chunk
attribute on the <map> element, which will apply to any
<topicref> that does not specify its own by-xxx
policy.
When no @chunk attribute values are specified or
defaulted, chunking behavior is implementation dependent. When variations of this sort
are not desired, a default for a specific map can be established by including a
@chunk attribute value on the <map> element.
When chunk processing results in new documents, the resource name or identifier for the new document (if relevant) is determined as follows:
<map> element), the resource name SHOULD be taken from the resource name of the
map.@copy-to attribute is specified, the resource name MUST taken from the @copy-to
attribute.@copy-to attribute is not specified and one or more keys
are specified on the <topicref>, the resource name SHOULD be constructed using one of the keys.@copy-to and @keys are not specified and the
by-topic policy is in effect, the resource name SHOULD be taken from the @id attribute of the
topic.@copy-to and @keys are not specified and the
by-document policy is in effect, the resource name SHOULD be taken from the resource name of the referenced document.When following these steps results in resource name clashes, processors MAY recover by generating alternate resource
identifiers. For example, when two chunked topics use the same @id
attribute, a processor could recover by combining the original resource name with the
@id value instead of using only the @id value.
Implementers MAY define their own custom, implementation-specific tokens. To avoid name conflicts between implementations or with future additions to the standard, implementation-specific tokens SHOULD consist of a prefix that gives the name or an abbreviation for the implementation followed by a colon followed by the token or method name.
For example: acme:level2
could be a token for the Acme DITA Toolkit that requests the
level2
chunking method.