draggable element must have an item slot

The slot global attribute assigns a slot in a shadow DOM shadow tree to an element: An element with a slot attribute is assigned to the slot created by the element whose name attribute's value matches that slot attribute's value. You can have multiple elements assigned to the same slot by using the same slot name. Elements without a slot attribute are assigned to the unnamed slot, if one exists.

Description: Create targets for draggable elements. ... The drop event will still bubble normally, but the event.target can be checked to see which droppable received the draggable element.

Before you can cast a spell, you must have the spell prepared in your mind or have access to the spell from a magic item, such as a Spell Scroll.