The <apipackage> element is a reference to a package.
This element can be used to reference a package from another DITA topic type.
<task id="httpxml">
<title>Getting an XML file through an HTTP connection</title>
<taskbody>
<steps>
<step><cm>Open the connection.</cm>
<info>You use <apipackage keyref="com.ibm.xtools.patterns.framework.uml2">com.ibm.xtools.patterns.framework.uml2</apipackage>
in a Java application.</info>
</step>
...
</steps>
</taskbody>
</task>