This is a filter I quickly wrote for so that I can have any php source that I put into content highlighted.

[?php
echo "hello world\n";
?]

Not only can you hilight code that is typed in but instead you can get the filter to include directly from another php source node.

This works much the same as how the project module does it, but I wanted it work with all modules, thus a filter would work alot better than how they have added it to the project module.