The <apiclassifier> element is a reference to a classifier.
The <apiclassifier> element can be used to reference a classifier 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 <apiclassifier keyref="java.net.URLConnection">URLConnection</apiclassifier>
in a Java application.</info>
</step>
...
</steps>
</taskbody>
</task>