Correction: The Restrict To
button, usually grayed-out, is on the far left
, on the same line as the Search field. It appears underneath the Add Books icon and above the Tag Browser's Find Tag field. At least this is the case on my visually non-modified system.
Perhaps theducks' window is different due to a theme or some kind of visual customization?
Restrict To works with saved searches. I had to ask about this myself and did so in the following topic: Way to Hide Search Bar
, from message #6 onward. (The original topic itself is about something completely different; the part about Restrict To only occurs from my question and onward.)