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 about half of the
letters hidden by underscores.
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 about half of the letters hidden by underscores.