Hi,
If you are using a WADL include the below fields highlighted in Bold. It should populate the contents when the document gets generated.
<method name="POST" id="postdata">
<doc xml:lang="en" title="postdata">Implemntation notes for the post data</doc>
<request>
<doc xml:lang="en">This data gets poppulated as "Description" on right side of text block</doc>
<representation mediaType="application/json">
<doc title="payload">
{ "name":"John", "age":30, "cars":[ "Ford", "BMW", "Fiat" ] }
</doc>
</representation>
</request>
<response status="200">
<representation mediaType="application/json"/>
</response>
</method>
</resource>