Minecraft wiki entry for Development_versions, associated text: Can collect the same items from the world as it holds in its hand.
If holds an item it got from a player, it will follow that player.
Able to drop items at nearby note blocks.
When playing a note block near them, that note block becomes their favorite one for 30 seconds, and they will attempt to drop off items at the note block rather than at the player.
If they have items in their inventory, they will attempt to give them to their owner.
Sometimes spawn in cages next to pillager outposts (similar to iron golem), and inside woodland mansions.