Show a real example, I don't know if by "regex" you mean "a string like a regex" or a "regex notation".

My `examples/sort.cf` commit uses these markers:

```cf3
#+begin_src cfengine3
...
#+end_src
```

What exactly would the macro have to say to include that file with those markers?  Help me out and I'll commit the example to https://github.com/cfengine/documentation/blob/master/README.md for you :)