The <cxxunion> element is a reference to a C++ union.
The <cxxunion> element can be used to reference a C++ union from another topic type.
<task id="connectionsxml">
<title>Connections</title>
<taskbody>
<steps>
<step><cm>Open the connection</cm>
<info>You can use <cxxunion keyref="unionkey">uConnection union</cxxunion>
in a C++ application.</info>
</step>
...
</steps>
</taskbody>
</task>