The <cxxClassBaseUnion> element declares inheritance from a base union in a class derivation.
Used within a <cxxClassDerivation> element to declare inheritance from a base union.
<cxxClassDerivation>
<cxxClassDerivationAccessSpecifier value="public"/>
<cxxClassBaseUnion href="union_base">Base</cxxClassBaseUnion>
</cxxClassDerivation>