Source Code Markup Language?

I've been googling around for an XML language that describes source 
code, but all I've found is an old SGML language. It's mostly out of 
curiosity, but I'd like to see if there's a simple language that merely 
marks up variables, constants, functions/methods, numbers, string, etc. 
Something along the line of

  <var>foo</var> <op>:=</op> <str>"foo"</str> <op>+</op> <str>"bar"</str>

The most important thing is that it should be possible to embed it in XHTML.

  <h:p xmlns="http://www.w3.org/1999/xhtml" xmlns:c="urn:code...">
    In the following example we assign <c:str>"foobar"</c:str> to 
<c:var>baz</c:var>.
  </h:p>

Do any of you know such a language?


Cheers,

Daniel Schierbeck