Maps with Topic Hierarchy
A map with a topic hierarchy contains topics with a parent or child relationship.
Tip: Topic hierarchies may be harder to reuse than map hierarchies. Map
hierarchies can be easily added to new maps, while topic hierarchies have to be rebuilt
each time.
Example
<map id="_m_user_guide" title="User Guide">
<topicref href="introduction.dita">
<topicref href="features.dita"/>
</topicref>
<topicref href="safety.dita"/>
...
</map>