Can't implement a SortableJS plugin without referencing unexported symbols from `sortablejs` source code

Question

I want to write a SortableJS plugin that gets mounted to a Sortable instance from the sortablejs package:

import Sortable from 'sortablejs'
Sortable.mount(new MyPlugin())

However, looking at the shipped plugins, it looks like they depend on unexported symbols imported directly from the source code. For example MultiDrag.js imports expando from ../../src/utils.js.

Can I write a plugin without referencing sortablejs source code?