This is pretty unintuitive. I would expect that if I'm on the meta category page my search is automatically limited to meta posts.

Also the category filter isn't very discoverable. "Q&A" and "Meta" aren't labeled as categories. "category" isn't listed in the quick help in the search drop down. Nothing on the search page says what a category is. If you figure out that category can be searched by, and know what a category is, you still can't search by that category until you look up the number for it.

That's way too many points to learn for something that should happen automatically.

That's a good point. It would be better to default to the current category (by adding it to the query shown on the results page), and then if you meant to search the whole community you could just delete that part.

We wanted to be able to specify categories by name rather than number, like with post types, but there was some technical issue when I asked about that. I've forgotten the details now and will try to find out.