When doing fill-in sentences reviews, I like to keep furigana off. However, sometimes there’s a single word that I’ll forget, and I just want to quickly check the furigana. I then have to take my hand off the keyboard to use the mouse to hover over it. I think it would be convenient if there were a hotkey we could press (either as a toggle or press-and-hold) to see the furigana for the sentence. I ask this because for basically anything else the user might want to do, there are hotkeys, whether it’s spacebar for seeing progressive hints, p for the audio, a for seeing the answer, f for scrolling down to the grammar or vocab point, etc.
I’ve done my own little thing for it (won’t bother spamming script stuff haha), but just something to think about. For me, I’ve done it such that if I tap shift, it just toggles the rt (furigana) opacity for the entire page (and site-wide, such that even when reading grammar points, I can do it all with just the keyboard, as you have already mapped hotkeys for right and left arrow for different pages, etc.). Tapping shift again will re-hide them. So basically just boolean not of opacity with repeat/hold debounce.
I think something like this might be useful for people who keep furigana off but just want to see them quickly for a sentence where they forgot one or something like that but don’t want to take their hands off the keyboard to hover over with the mouse.