Loop type=post category=?

Yeah, the current docs are a little sparse on how-tos and examples. I’m actually currently working on some revised docs that should launch within the next week (I expect you’ll get an email about it) that are going to include a lot more examples. As far as forum posts, I found this thread and this one that mention displaying posts based on multiple category/taxonomy terms. The parameters I mentioned/linked to in my earlier post will definitely allow you to achieve what you’re trying to do.

I’m going to add some examples to the new docs soon to demonstrate how you’d use these parameters together so here’s one I just put together. Hopefully this will help you understand how all those parameters work together to allow you to write complex rules for which taxonomy terms should/shouldn’t have their posts displayed. The example below would show posts in an “event” post type that have the category term “seminar” applied and also don’t have either the terms “workshop” or “training” applied:

<Loop type=event taxonomy=category terms=seminar taxonomy_relation=and taxonomy_2=category taxonomy_compare_2=not terms_2=workshop,training>