main_template now uses Zope 3 viewlets
If have previously shipped customized versions of templates like header.pt, viewThreadsAtBottom.pt or global_contentmenu.pt to get things into the page, please switch to viewlets instead, as it makes it much easier for multiple products to co-exist without stepping on each others changes.
Documentation and examples can be found in "this tutorial":http://plone.org/documentation/tutorial/customizing-main-template-viewlets.

