code: function isDropAllowed(itemType) {
          if (listSettings.disabled) return false;
          if (!listSettings.externalSources && !dndState.isDragging) return false;
          if (!listSettings.allowedTypes || itemType === null) return true;
          return itemType && listSettings.allowedTypes.indexOf(itemType) != -1;
        }
docs: Checks various conditions that must be fulfilled for a drop to be allowed, including the
  dnd-allowed-types attribute. If the item Type is unknown (null), the drop will be allowed.