<strike>deleted text</strike>
to get <literal>..</literal>
tags around blocks of HTML to avoid accidental interpretation of Wiki syntax within the HTML.
<body>
and </body>
tags.
<p />
paragraph tags on empty lines, which causes problems if done between HTML tags that do not allow paragraph tags, like for example between table tags.
<...>
- of a HTML tag are on the same line, or the tag will be broken.