I'm trying to append multiple categories together in the URL query parameter, "category", but I don't know how to make it work so that I can filter the search results with multiple categories.

For example, let's say I'm looking for a series that are tagged with both categories, "Dream/s" and "Robot/s". I thought you can append them together in the "category" parameter, like "Dream/s_Robot/s", or "Dream/s+Robot/s", but none of these formats work. I don't know how to really do this.

If this isn't a feature, can we add this ability to search and filter for multiple category tags?

if im understanding you, you can already do this with the "advanced search" function, which you can find under the search bar. after you click advanced search, scroll down to where it says "Categories/Tags" and that's where you can add multiple tags, but you have to do only add tag per line so it's like this:

Robot/s
Dream/s

and this is what i was told to do if you want to exclude tags, for example like Age Gap, put a - in front of the tag you don't want, so your search looks like this:

Robot/s
Dream/s
-Age Gap

the - won't work for series that don't have those tags of course so i'll still get "age gap" if someone doesn't tag the series as such even if it's true when you read it... if you're looking for things on manga updates in the future, don't search with the "female protagonist" or "male protagonist" tags because they're very underused and you'll miss a lot of things because each of those number only to about 2000 when there are obviously much more manga on here. feel free to add those tags yourself for series that you see that don't have those two tags if you want.

I see. It works. That's good to know. Thanks again for your help.