If you copy a block with ctrl and middle click of the mouse, it contains the nbt+ of the copied block. Works with command blocks, ovens, etc. Except of the chiselled bookshelves, however, they are empty of texture despite the fact that it should be full. But filled with books when you dismantle it. Found in 1.20.1 (singleplayer) reviewed in the same world in 23w51b.