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Language reference: All-inclusive edition
The language reference portion of the DITA specification contains a topic for each DITA element. The topic defines the element, its inheritance hierarchy, and provides examples of usage. This portion of the DITA specification also includes information about DITA attributes.
Classification elements
Classification elements support managing metadata. Those in the subject scheme map are used to define controlled values and to bind the controlled values to DITA attributes as enumerations. Those declared in the classification domain are used in other maps to classify content according to the scheme.
Subject scheme elements
Subject scheme maps are used to define sets of controlled values and taxonomic subjects; bind controlled values to attributes; and specify relationships among taxonomic subjects.
<defaultSubject>
The <defaultSubject> element is used within an attribute enumeration to set the default value for the attribute in cases where no value is specified for the attribute. The default subject must be one of the controlled values that are bound to the attribute.

Specification URIs
Notices
Introduction to DITA 1.3
The Darwin Information Typing Architecture (DITA) specification defines a set of document types for authoring and organizing topic-oriented information, as well as a set of mechanisms for combining, extending, and constraining document types.
Architectural specification: All-inclusive edition
The architectural specification portion of the DITA specification outlines the framework of DITA. It contains an overview of DITA markup; addressing; processing; configuration, specialization, generalization, and constraints; as well as information about coding DITA grammar files.
Language reference: All-inclusive edition
The language reference portion of the DITA specification contains a topic for each DITA element. The topic defines the element, its inheritance hierarchy, and provides examples of usage. This portion of the DITA specification also includes information about DITA attributes.
- Element quick reference
  This section contains a listing of DITA elements.
- Topic elements
  The base topic elements include elements that make up the core building blocks of the DITA topic, such as topic, body, and related-links, as well as elements like <p> and <ph> that are used in many topic specializations. Some of these elements are also available inside the <topicmeta> map element.
- Map elements
  Map elements include the core components of DITA maps, such as <topicref> and <reltable>, as well as general purpose map specializations in the map group domain.
- Metadata elements
  Metadata elements include information that is located within the <topicmeta> element (in maps) or <prolog> element (in topics), as well as indexing elements that can be placed in additional locations within topic content.
- Domain elements
  General purpose domains are not specific to any type of information, such as the hazard statement domain that provides elements for describing hazardous situations.
- Classification elements
  Classification elements support managing metadata. Those in the subject scheme map are used to define controlled values and to bind the controlled values to DITA attributes as enumerations. Those declared in the classification domain are used in other maps to classify content according to the scheme.
  - Subject scheme elements
    Subject scheme maps are used to define sets of controlled values and taxonomic subjects; bind controlled values to attributes; and specify relationships among taxonomic subjects.
    - <subjectScheme>
      The <subjectScheme> element is a specialization of <map>; it defines taxonomic subjects and controlled values.
    - <schemeref>
      A <schemeref> element references another subject scheme map. Typically, the referenced subject scheme defines a base set of controlled values; the referencing map then extends the base set of controlled values. The values specified in the subject scheme maps are merged; the result is equivalent to specifying all of the values in a single map.
    - <hasInstance>
      The <hasInstance> element specifies that the contained subjects have an INSTANCE-OF relationship with the container subject. In an INSTANCE-OF hierarchy, the child subject is a specific entity or object and the parent subject is a type, kind, or class of entity or object.
    - <hasKind>
      The <hasKind> element specifies that the contained hierarchy expresses KIND-OF relationships between subjects.
    - <hasNarrower>
      For subjects within the <hasNarrower> element, the container subject is more general than each of the contained subjects. That is, this element makes the default hierarchical relationship explicit, although the way in which a relationship is narrower is not specified.
    - <hasPart>
      The <hasPart> element specifies that the contained hierarchy expresses PART-OF relationships between subjects.
    - <hasRelated>
      The <hasRelated> element identifies an associative relationship between the container subject and each of the contained subjects.
    - <enumerationdef>
      The <enumerationdef> element identifies one attribute and one or more categories that contain the controlled values for the enumeration. The @type attribute has a default value of "keys".
    - <elementdef>
      The <elementdef> element identifies an element to which an attribute is bound. If the <enumerationdef> element does not contain an <elementdef> element, the enumeration is bound to the attribute in all elements.
    - <attributedef>
      The <attributedef> element specifies the attribute that is bound to a set of controlled values. This binding restricts the permissible values for the attribute to those that are contained in the set of controlled values.
    - <defaultSubject>
      The <defaultSubject> element is used within an attribute enumeration to set the default value for the attribute in cases where no value is specified for the attribute. The default subject must be one of the controlled values that are bound to the attribute.
    - <subjectHead>
      The <subjectHead> element provides a heading for a group of subjects, for use if the scheme is displayed. For instance, a scheme might be displayed to let a user select subjects as part of faceted browsing. The <subjectHead> element itself does not reference a file and cannot be referenced as a key, so it does not define any controlled values.
    - <subjectHeadMeta>
      The <subjectHeadMeta> element allows a navigation title and short description to be associated with a subject heading.
    - <subjectdef>
      The <subjectdef> element defines a subject (also known as a controlled value) within a subject scheme. The @keys attribute specified on the <subjectdef> element assigns a key to the subject. A subject with a key can be addressed using a @keyref attribute.
    - <relatedSubjects>
      The <relatedSubjects> element establishes associative relationships between each child subject and every other child subject (unless the association is restricted by the @linking attribute of the subjects).
    - <subjectRelTable>
      The <subjectRelTable> element is a specialized relationship table which establishes relationships between the subjects in different columns of the same row. This element provides an efficient way to author non-hierarchical relationships between subjects. Tools (such as search tools) that use subject relationships to find related content might use these associative relationships in a similar way to the hierarchical relationships.
    - <subjectRelHeader>
      The <subjectRelHeader> element specifies the roles played by subjects in associations.
    - <subjectRel>
      The <subjectRel> element contains a set of subjects that are related in some manner. Each group of subjects is contained in a <subjectRole> element; the associations between different columns in the same row are evaluated in the same way as those in a <relrow> (from which <subjectRel> is specialized) but define relationships between the subjects instead of links between topic documents.
    - <subjectRole>
      The <subjectRole> element, when used within a <subjectRel> element, contains a set of subjects that are related to other subjects in the same row of the current <subjectRelTable>. By default, no relationship is defined between multiple subjects in the same <subjectRole> element. When used within the <subjectRelHeader>, the <subjectRole> element defines the category of subject or relationship provided by that column.
  - Classification domain elements
    The classification domain elements are used to identify the subject matter of content that is referenced in a map. These subjects must be subjects defined in a subject scheme map. In particular, this allows an author to classify content in new subject categories that are not bound to existing metadata attributes.
- Specialization elements
  Several DITA elements exist either for architectural reasons or for support of specialized markup yet to be designed. Although there is little need to use these elements unless you are directed to, some of them, such as <state>, can be used if your content makes use of these semantic distinctions. For example, a discussion of signals on a gate of an integrated logic circuit might use the <state> element to represent either on or off conditions of that gate.
- Legacy conversion elements
  Conversion elements exist primarily to aid in the conversion of content to DITA.
- DITAVAL elements
  A conditional processing profile (DITAVAL file) is used to identify which values are to be used for conditional processing during a particular output, build, or some other purpose. The profile should have an extension of .ditaval.
- Technical content elements
  Elements in the technical content section include the original Concept, Task, and Reference specializations, as well as specializations added in later releases. It also includes domains designed primarily for technical content.
- Learning and training elements
  Elements in the learning and training section include specialized topics, maps, content, and metadata elements specially designed to support instructional content.
- Attributes
  This section collects commonly used attributes, with common definitions. If an element uses a different definition, or narrows the scope of, an otherwise common attribute, it will be called out in the topic that defines the element.
Conformance
Conformance to the DITA specification allows documents and document types that are used with different processors or different versions of a processor to produce the same or similar results with little or no reimplementation or modification.
Acknowledgments
(Non-normative) Many members of the OASIS DITA Technical Committee participated in the creation of this specification and are gratefully acknowledged.
Non-normative information
This section contains non-normative information, including topics about new features in DITA 1.3 and migrating from DITA 1.2 to DITA 1.3.
Content models for learning and training package
For each element in the learning and training package, this section presents the content model and a list of parent elements that can contain that element.

`<defaultSubject>`

The <defaultSubject> element is used within an attribute enumeration to set the default value for the attribute in cases where no value is specified for the attribute. The default subject must be one of the controlled values that are bound to the attribute.

Content models

See appendix for information about this element in OASIS document type shells.

Inheritance

- map/topicref subjectScheme/defaultSubject

Example

The following example declares that each of the four defined "os" values is valid within the @platform attribute; if no value is specified, the default is "linux".

<subjectScheme>
  <subjectdef keys="os">
    <subjectdef keys="linux"/>
    <subjectdef keys="mswin"/>
    <subjectdef keys="zos"/>
    <subjectdef keys="macos"/>
  </subjectdef>
  <enumerationdef>
    <attributedef name="platform"/>
    <defaultSubject keyref="linux"/>
    <subjectdef keyref="os"/>
  </enumerationdef>
</subjectScheme>

Attributes

The following attributes are available on this element: Universal attribute group, Link relationship attribute group (with a narrowed definition of @href, given below), Topicref element attributes group, outputclass, @keys, and @keyref. This element also uses @processing-role, @locktitle, and @toc from Attributes common to many map elements.

@href: A pointer to the resource represented by the <topicref>. See The href attribute for detailed information on supported values and processing implications. References to DITA content cannot be below the topic level: that is, you cannot reference individual elements inside a topic. References to content other than DITA topics should use the @format attribute to identify the kind of resource being referenced.