(map mapgroup-d) The <topichead> element provides a title-only entry in a navigation map, as an alternative to the fully-linked title provided by the <topicref> element. Category: Mapgroup elements The <topicgroup> element is for creating groups of <topicref> elements without affecting the hierarchy, as opposed to nested < topicref> elements within a <topicref>, which does imply a structural hierarchy. It is typically used outside a hierarchy to identify groups for linking without affecting the resulting toc/navigation output. Category: Mapgroup elements The contents of an <anchorref> element are rendered both in the original authored location and at the location of the referenced <anchor> element. The referenced <anchor> element can be defined in the current map or another map. The <mapref> element is a convenience element that has the same meaning as a <topicref> element that explicitly sets the format attribute to "ditamap". The hierarchy of the referenced map is merged into the container map at the position of the reference, and the relationship tables of the child map are added to the parent map. The <topicset> element defines a complete unit of content that can be reused in other DITA maps or other <topicset> elements. The <topicset> element can be especially useful for task composition in which larger tasks that are composed indefinitely of smaller tasks. The id attribute on a <topicset> is required, which ensures that the complete unit is available for reuse in other contexts. The <topicsetref> element references a <topicset> element. The referenced <topicset> element can be defined in the current map or in another map. The <keydef> element is a convenience element that is used to define keys without any of the other effects that occur when using a <topicref> element: no content is included in output, no title is included in the table of contents, and no linking or other relationships are defined. The <keydef> element is not the only way to define keys; its purpose is to simplify the process by defaulting several attributes to achieve the described behaviors.