Webpack ā€” When building a code bundle, and subsequently importing it, how do I access named exports?

Iā€™m building a custom version of CKEditor which uses webpack (v4) to bundle the src into a minified bundle. My src includes both default and named exports, along the lines of:

export default class MyEditor extends ClassicEditor {}
export class InteractiveMyEditor extends ClassicEditor {}
export const Context = CKContext

The webpack.config.js file includes the following output section

output: {
  library: 'MyEditor',
  path: path.resolve( __dirname, 'build' ),
  filename: 'ckeditor.js',
  libraryTarget: 'umd',
  libraryExport: 'default'

it all builds fine and I can

import MyEditor from '@project/ckeditor-build-myeditor'
// MyEditor is defined

just fine.

But I can't access the InteractiveMyEditor or the Context objects

import { Context, InteractiveMyEditor } from '@project/ckeditor-build-myeditor'
// both Context and InteractiveMyEditor are undefined

I've been trying to make sense of the Webpack4 Docs but can't see what else to do other than try different values for libraryTarget. I've tried commonjs, and 'module just to see if that helped but alas no.

How do I export the named exports correctly?