The Devel module is such an indispensable part of any Drupal developer's toolkit that it's easy to forget that it does sometimes tinker with Drupal at a fairly low level. I was getting a perplexing error from an XML-RPC service I was developing as part of a Drupal module.

I just encountered a problem arising from a combination of the TinyMCE WYSIWYG module and the FAQ module in Drupal 6.

In a nutshell:

If you want to see what's going on when Drupal's cron.php script runs, one thing you can do is to set a breakpoint in a module's implementation of the hook_cron() function, and call cron.php directly from your debugger. There you can step through your breakpoints, examine variables, and hopefully zero in on your problem.

The Drupal Form API is a wonderful thing... once you've been using it long enough, it's easy to forget all of the laborious validation and post-submit processing you used to do by hand for each and every HTML form in your solution.

The FAPI does things its own way, though, and if you're building especially complex forms that involve multiple steps or dynamically generated options, you may encounter the following error upon submitting your form: