itemdef = {
    -- just started wielding
    _on_select = function(itemstack, player) end, --> return ItemStack to modify or nil
    -- just stopped wielding
    _on_deselect = function(itemstack, player) end, --> return ItemStack to modify or nil
    -- every step while wielded
    _on_step = function(itemstack, player, dtime) end, --> return ItemStack to modify or nil
    -- every step whether wielded or not
    _on_inventory_step = function(itemstack, player, dtime, list_name, list_index) end,
    -- on this item moved to another index and/or list
    --[[
        info = {
            action = "move" | "put" | "take"
            stack = ItemStack, -- the stack that is the thing being moved
            [to,from]_stack = number|nil, [to,from]_index = number|nil,  [to,from]_list = string|nil,
            count = number|nil,
            -- to_stack means the stack that is not changed yet but will have the stack added to
        }
    --]]
    _on_inventory_move_allow = function(itemstack, player, info) end, --> return 0 to cancel or num of items to allow
    -- on this item moved to another index and/or list
    _on_inventory_moved = function(itemstack, player, info) end,
    -- before creating an item entity
    _on_drop = function(itemstack, player) end, --> return ==false to cancel
    -- after creating an item entity
    _on_dropped = function(itemstack, player, object) end,
    -- when in an inventory list that is registered as an equipment list (e.g. armor, accessories)
    _on_equipment_step = function(itemstack, player, dtime, list_name, list_index) end,
    -- when first moved to equipment list
    _on_equipped = function(itemstack, player, info) end, --> void
    -- when moved from equipment list
    _on_unequipped = function(itemstack, player, info) end, --> void
    -- circumvents / stands in for `core.get_node_drops`
    _get_node_drops = function(node, toolname) end --> list of itemstacks: table[i] = ItemStack
}

-- If any slot has a bound group name, no other items may be moved there. You may bind multiple groups to one slot/list.
itemextensions.bind_group_to_inventory_list(item_group_name, inventory_list_name)
itemextensions.bind_group_to_inventory_slot(item_group_name, inventory_list_name, list_index)

-- There is no change allowed for this callback but you can manually edit the inventory if needed.
-- Note however, that this callback will run a second time if you modify the stack.
itemextensions.register_on_any_item_changed(function(itemstack, player, listname, listindex, oldstack) end) 

-- Note that it is possible the stack is not in its original form by the time your callback runs on it.
-- This is the case for all of the below. Return a second argument of true to stop further callbacks in this stack.
-- Callbacks are run regardless of whether the name has changed otherwise.

-- This item name moved index and/or list
itemextensions.register_on_move_item("my_mod:my_item", function(itemstack, player, info)
    return ItemStack or nil, true or nil
end)
-- Any item is now wielded
itemextensions.register_on_select(function(itemstack, player)
    return ItemStack or nil, true or nil
end)
-- Any item is no longer wielded
itemextensions.register_on_deselect(function(itemstack, player)
    return ItemStack or nil, true or nil
end)
-- While item is wielded, on and after `select`ed and before `deselect`ed
itemextensions.register_on_wield_step(function(itemstack, player, dtime)
    return ItemStack or nil, true or nil
end)