Searching for Multiple Subcategories
 

I have a custom navigation where clicking subcategories will link to the search results page and show subcategories. I can get it to search for 1 subcategory using this URL:


I tried to change include/search.php, but that file is too interconnected to augment.

What I am looking for is a query string by which I can simply search for multiple subcategories. Something like this:


or by name if that's easier:


Thanks in advance for any help provided!