Generate a hint about the back of a flashcard, to display if the user asks for it.
For a language-vocabulary flashcard with a word or phrase in one language on front and a word or phrase in another language on back,
the hint is the back with some letters hidden by underscores.
Returns
a hint providing some (but not all) of the information from the back of the card, as described above,
or undefined if no hint can be generated for this card.
Generate a hint about the back of a flashcard, to display if the user asks for it.
For a language-vocabulary flashcard with a word or phrase in one language on front and a word or phrase in another language on back, the hint is the back with some letters hidden by underscores.
Returns
a hint providing some (but not all) of the information from the back of the card, as described above, or undefined if no hint can be generated for this card.