Just a heads-up, folks:
Later this week I'm going to be installing a fix for some longstanding bugs with HTML in wiki pages. One of the issues is a difference in rendering of templates that improperly nest HTML tags, which caused certain badly-written templates to render in one way on Wikipedia but wildly broken on most other wikis.
(Don't forget that an important part of what Wikipedia & its sister projects are about is making information sharable and reusable. If the code breaks when copied to another site, that's Bad.)
Once the fix is in, templates should render about the same on Wikipedia and other wikis where the "HTML Tidy" plugin isn't being used. The bad news is that some of these templates will be broken; so it would be great if we can make sure they get cleaned up.
Problem templates are mostly those which start an HTML tag in one template, then finish it in another. For instance if {{table-header}} contains a <table>, and then the table rows and final </table> are in another template entirely. These have always broken on regular MediaWiki -- the template is required to close its own tags -- though they sometimes appeared to work on Wikipedia due to bugs with our HTML handling when Tidy is enabled.
I've done some automated checks on templates on en.wikipedia.org to make a list of likely problem candidates:
http://leuksman.com/misc/templates/html-table-start.txt http://leuksman.com/misc/templates/html-table-end.txt http://leuksman.com/misc/templates/html-table-row.txt
If you've got a template that you're not sure if it will work, try copying it to my test wiki at http://test.leuksman.com/ . This has the fix installed with the corrected behavior, so you can see about how it will render on Wikipedia next week.
Please make sure this information is disseminated to the various other language and project wikis people are working on; I don't want to hear "waah! all my templates broke and no one told me!" next week. :)
For the moment the same kind of construct with wiki tables ({| ... |}) will still work, but note that some time in the future we're going to have to look at 'fixing' that too. (This might require some enhancements to how templates work to make it easier to fill in long tables.)
-- brion vibber (brion @ pobox.com)