[Xymon] Any docs on how to write tests?

Looking for a way to write tests that check a URL, and return fail/pass depending on the content.

I could easily use curl to do this, but I'm looking for information on how to integrate the curl command line into xymon as a test.

So far as I can see, the bb-services file only accepts test definitions by port, but I may be missing something.

Thanks in advance!

-Bobby