I wrote a feature at Wikimania and forgot to announce it outside that audience. It's live now on Wikimedia websites. The feature is the ability to control template inclusion by the use of <noinclude> and <includeonly> tags.
Anything between <noinclude> and </noinclude> will be processed and displayed only when the page is being viewed directly, not included. Possible applications are:
* Categorising templates * Interlanguage links to similar templates in other languages * Explanatory text about how to use the template
The converse is <includeonly>. Text between <includeonly> and </includeonly> will be processed and displayed only when the page is being included. The obvious application is:
* Adding all pages containing a given template to a category
Note that the usual update problems apply -- if you change the categories inside a template, the categories of the referring pages won't be updated until those pages are edited.
Beware of bugs: this hasn't been tested in a real wiki environment yet.
-- Tim Starling