ItemStack:is_empty(): return true if stack is empty
ItemStack:get_name(): returns item name (e.g. "default:stone")
ItemStack:get_count(): returns number of items on the stack
ItemStack:get_wear(): returns tool wear (0-65535), 0 for non-tools
ItemStack:get_metadata(): returns metadata (a string attached to an item stack)
ItemStack:clear(): removes all items from the stack, making it empty
ItemStack:replace(item): replace the contents of this stack (item can also be an itemstring or table)
ItemStack:to_string(): returns the stack in itemstring form
ItemStack:to_table(): returns the stack in Lua table form
ItemStack:get_stack_max(): returns the maximum size of the stack (depends on the item)
ItemStack:get_free_space(): returns get_stack_max() - get_count()
ItemStack:is_known(): returns true if the item name refers to a defined item type
ItemStack:get_definition(): returns the item definition table
ItemStack:get_tool_capabilities(): returns the digging properties of the item,
^ or those of the hand if none are defined for this item type
ItemStack:add_wear(amount): increases wear by amount if the item is a tool
ItemStack:add_item(item): put some item or stack onto this stack,
^ returns leftover ItemStack
ItemStack:item_fits(item): returns true if item or stack can be fully added to this one
ItemStack:take_item(n): take (and remove) up to n items from this stack
^ returns taken ItemStack
^ if n is omitted, n=1 is used
ItemStack:peek_item(n): copy (don't remove) up to n items from this stack
^ returns copied ItemStack
^ if n is omitted, n=1 is used