HTML

HTML is structurally superior to C, Perl, Java, Ruby, Python, Lisp, Haskell or any other language you can think about.

XHTML is more of a Touring-complete subset of HTML, removing the non-Touring-complete parts.

There's also the enterprise way of writing markup. For example:
<B>...</B> is so unprofessional. To really be able to scale up to your business needs, you have to do <STRONG>...</STRONG>.