A curiosity :)
When we shifted our project to using reST, I extended it in some ways, like being able to use triple-stars to emphasize + strong content. Because --- people thinking visually --- would need to do that some times.
For some reason, much later, I found myself reading the docutils list, where a reST advocate strongly emphasized that this made no sense. "**" was "strong emphasis", so what (structurally, semantically, ?) sense did "strong emphasis" + "emphasis" make? And he was right: it doesn't really make any sense ... except it was definitely necessary.
(And, um, I'd have to confess that the idea of generating smileys always seemed cool until the unbalanced paren problem became obviouis. Me, I can't stand the look of smileys in proportional fonts ;-)