Please note:
HTML will be purified, but we allow for a number of HTML tags so that you have the flexibility to decorate your comment text to some extent. The comments allow the following HTML tags:

strong, b, em, blockquote, a, code, pre

To put code into your comment, simply encapsulate your code with
[code language="XXX"][/code], where XXX is any common language, for instance "PHP", "SQL", "C", etc.