So the type of narrowing you’re looking for doesn’t exist, but in case you haven’t seen it there is actually a way to slightly narrow the main search by clicking the icon on the left of the search bar. This toggles between searching cards by everything, title, content, or tags (but actions/commands will always be searched regardless). You can also toggle by pressing the tab button.
Text-based operators are always a bit hard in a search like this one because there is the potential that users want to actually search for whatever operator literal you decide to use (e.g. colons).