union.xml

<!-- based on xproto -->
<xcb header="union">

  <union name="ClientMessageData">
    <!-- The format member of the ClientMessage event determines which array
         to use. -->
    <list type="CARD8"  name="data8" ><value>20</value></list> <!--  8 -->
    <list type="CARD16" name="data16"><value>10</value></list> <!-- 16 -->
    <list type="CARD32" name="data32"><value>5</value></list>  <!-- 32 -->
  </union>

</xcb>