I often have to look at the project's README to remember how to use Cardinal. The README also doesn't cover everything, there's some stuff that's less discoverable like the newly added shorthand aliases for tag and infolder filters.
Would you consider having a cheatsheet, embedded or pop-up, that documents the keyboard shortcuts and search operators? It can be accessible via the ? key when the search field isn't in focus (see GitHub and Gmail examples below), and it can also be accessible via the menu, e.g. "View" > "Cheatsheet" or "Help" > "How to use".
