app/views/codes/_item.xml.erb
<Code isUniversallyUnique="true">
<%= render 'exports/exploded_urn', object: code, reference: false %>
<% if code.category %>
<r:CategoryReference>
<%= render 'exports/exploded_urn', object: code.category, reference: true %>
</r:CategoryReference>
<% end %>
<r:Value><%= code.value %></r:Value>
</Code>