I keep forgetting how to construct the very useful combinations of taxonomy terms in Drupal. I feel as if these tricks are not as well documented, or perhaps exposed in the user interface, as they could be.
There are two forms I’m aware of, at least with the taxonomy module in Drupal 5.2.
The form with taxonomy termids separated by a comma gives an overlap of the terms. It’s the equivalent of asking for nodes which contain both the first time and the second term.
/taxonomy/term/1,2
The plus sign form results in a list of nodes with either the first term or the second term.
/taxonomy/term/1+2
I don’t know how far you can extend the list of terms, but I’ve personally tried as many as five.
Unfortunately, I’m not aware of a good way to find what terms match up to which termids.
Also, although you do get an RSS feed indicator, it directs to the RSS feed for the entire site. (I thought somewhere that I’d found a way to get a unique RSS feed for each such query.)
You can also specify the depth, as per this Drupal support posting.
/taxonomy/term/termids/depth
… where the termids, of course, are the termid numbers, as seen above, and the depth is how deep you want to go in a nest hierarchy of taxonomy terms. For depth, 0 is the same as not specifying a depth and “all” includes all subterms. Any number in between limits the depth.