This feature was exclusively part of a joke version and is not currently planned for addition to regular Minecraft. It is documented here on the wiki due to being officially-released content by Mojang Studios, even if not present in a final version.
Once the dupe_hack_occurrence_chance vote is approved the dupe hack item has a random chance of dropping whenever an entity with chests is killed by a player, e.g. when destroying a minecart with chest with a sword.
It doesn't appear in the creative menu, not even when the option "Operator Items Tab" is enabled, but can be given to the player with /give and other commands.
Usage[]
The dupe hack item can be used to create a limited amount of duplicate items by placing it on a crafting table with any other item. It has a random chance of breaking, controlled by the dupe_hack_break_chance vote. This limitation can be mostly bypassed by putting the items in an ender chest first and duplicating the chest.
When using the Dupe Hack, it has a random chance of breaking, which is often decided by votes.
Added minecraft:dupe_hack.