For some (user) talk pages, users want to add e.g. borders around all the content and do this by opening something like a <div style="border:1px solid gray;"> leaving it unclosed, so that all new comments appear to be inside of these borders (see an example from ptwiki). In such cases users consider it convenient to omit the end tag, because if they closed it, new comments would be after the borders, and they would need to move the end tag manually afterwards.
Is there a good/supported way to do this without introducing errors?