Robert Rohde wrote:
Actually, if one is following the HTML4 spec then <pre> would be expected to nest. (Not particularly useful as far as I can see, but it is what it is.)
<pre> in wikitext is explicitly not the same as <pre> in HTML. Unlike in HTML, HTML-like tags which appear inside <pre> are considered to be literal and are escaped. This behaviour is often used.
-- Tim Starling