It's difficult to understand what a ruleset has actually selected. I'm writing this one as vague because there could be many solutions.

More detail on the problem I faced. I didn't realize that I needed to click into the selector field to see the hover state on affect canvas objects. I thought I might get to hover on the field, or click the hint text "1 object selected". Hover did nothing, and clicking the text took me to the docs. Furthermore, even after giving the selector field focus, the hover state on affected objects goes away if I interact with the canvas, and doesn't return until I click out of that field and back into it.

A more sane solution would be a more consistent indicator on canvas when I interact with the selector field, or some kind of list of objects under the selector field, again paired with a canvas visualization.