That wholly depends on which approach you want to take… filter the
whole part, just process a piece of it, or do it after the fact.
If you want to filter the whole part, take a look at the built-in
Markdown and Textile filters. They take a very simple approach, which
is to take the rendered text and pass it directly to an external engine
(The Sass filter takes this approach too).
If you want to process just a piece, the approach would be to write a
global tag that does the filtering for you. This is the approach of the
original Syntax Highlighting behavior in 0.5.x, which provided an
<r:code/> tag, within which you would place your code.
highlighting on the client side. They’re perhaps not as robust as a
server-side version, but in many cases they do exactly what you need.
Dan W. has one: http://projects.danwebb.net/wiki/CodeHighlighter
Hope this helps!