Editing Template:Documentation/doc (section)

===On the Template page===
<pre>
Template code<includeonly>Any categories to be inserted into articles by the template</includeonly><noinclude>
{{documentation}}</noinclude>
</pre>

Note that, depending on the template, you may need to add a clear or complete a table/div just before <code><nowiki>{{documentation}}</nowiki></code> is inserted (within the noinclude tags).

The line break is also useful as it helps prevent the documentation template "running into" previous code.