A large red banner appears that says “Recursive transclusion error in transclude widget.” (If you're in preview mode creating a new tiddler, the error won't appear until you save the tiddler under some conditions.) This is a rather cryptic error message, but if you remember what it means, the cause of the error is usually obvious once you start looking.

As we move forward into templates, you will sometimes see this error on a template – in that case, it does not necessarily mean you did anything wrong. More to come.