[Manichean]

I just ran into a problem trying to use a custom binary column for distinguishing between my study textbooks and, well, every other ebook. My plan was to use the column to indicate whether a specific book is a textbook (=true) or not (=false), and then build a saved search to restrict library view to only textbooks or only every other kind of book. But while building the search pattern I ran into the problem: I've found that searching for col:true returns all books with a set value, be it true or false, while col:false returns every undefined book. But searching for actual values doesn't work: Every time I try to search for col:yes, col:no or any variation I could think of I'd get an empty search result (and yes, there are some books with each value set). So, my question is: How do you actually search for books with a specific value in a binary metadata field?