Can I take a discarded tile back?

Once the tile has been fully named or touches the table, it cannot be taken back.

More details

Question: I've started to discard, fully named the tile but not placed it on the table yet. I've just noticed a joker exchange is available. Can I exchange for the joker?

Answer: Sorry, your tile has been discarded. Once a tile has been fully named or it touches the table, it cannot be taken back to make a joker exchange.