##### 3.1.6.5 index-base

The <index-base> element allows indexing extensions to be added by specializing this element.

The <index-base> element can only exist as a child of an <indexterm> element. This characteristic makes it the appropriate element to specialize to add indexing extensions. For example, the index-see, index-see-also, and index-sort-as elements only make sense as children of <indexterm> and so are specializations of <index-base>. Those elements are all part of the indexing domain.

On its own, <index-base> has no meaning. Processors should ignore this element and its content if encountered in its unspecialized form.

###### Contains

Doctype | Content model
topic (base), map (base), classifyMap, subjectScheme, learningAssessment, learningBookmap, learningContent, learningMap, learningOverview, learningPlan, learningSummary | ( text data or data or data-about or foreign or unknown or keyword or term or indexterm) (any number)
topic (technical content), map (technical content), concept, ditabase, glossary, glossentry, glossgroup, reference, task, bookmap | ( text data or data or data-about or foreign or unknown or keyword or apiname or option or parmname or cmdname or msgnum or varname or wintitle or term or abbreviated-form or indexterm) (any number)
machineryTask | ( text data or data or data-about or foreign or unknown or keyword or wintitle or term or indexterm) (any number)

###### Contained by

Doctype | Content model
topic (base), map (base), topic (technical content), map (technical content), concept, ditabase, glossary, glossentry, glossgroup, reference, task (strict), task (general), bookmap, classifyMap, subjectScheme, machineryTask, learningAssessment, learningBookmap, learningContent, learningMap, learningOverview, learningPlan, learningSummary | indexterm

###### Inheritance

- topic/index-base

###### Example

The <index-see-also> element is specialized from index-base; see 3.1.3.2.4 index-see-also for an example of how index-base may be used with specialization.

###### Attributes

Name | Description | Data Type | Default Value | Required?
keyref | Keyref provides a redirectable reference based on a key defined within a map. See 3.4.2.3 The keyref attribute for information on using this attribute. | CDATA | #IMPLIED | No
univ-atts attribute group (includes select-atts, id-atts, and localization-atts groups) | A set of related attributes, described in 3.4.1.3 univ-atts attribute group |  |  |
global-atts attribute group (xtrf, xtrc) | A set of related attributes, described in 3.4.1.2 global-atts attribute group |  |  |
class | A common attribute described in 3.4.1.9 Other common DITA attributes |  |  |

Previous Topic: 3.1.6.4 foreign

Next Topic: 3.1.6.6 itemgroup

Parent Topic: 3.1.6 Specialization elements

Sibling Topics:

3.1.6.1 boolean

3.1.6.2 data

3.1.6.3 data-about

3.1.6.4 foreign

3.1.6.6 itemgroup

3.1.6.7 no-topic-nesting

3.1.6.8 state

3.1.6.9 unknown