The API documentation for Quill.import is misleading (emphasis mine):

Static method returning Quill library, format, module, or theme. In general the path should map exactly to Quill source code directory structure.

And the example has a comment that using Quill.import is…

// Similar to ES6 syntax import Link from 'quill/formats/link';

No other discussion is provided regarding exceptions to the "in general". So when I needed to get a non-default export that exists inside the "Quill source code directory structure" at blots/block I guessed I would have to do something like

let { BlockEmbed } = Quill.import('blots/block');    // WRONG

…and the Quill.import internals would have set things up so that all the other exports would be exposed as properties on the Block as default value it returns. But BlockEmbed gets an undefined value; apparently not much similarity to ES import as claimed.

Elsewhere in the documentation, I found a more helpful note:

You can view a list of Blots and Attributors available by calling console.log(Quill.imports);. Direct modification of this object is not supported. Use Quill.register instead.

So the secret is that Quill.import actually has very little to do with filesystem paths and ES module syntax, and a whole lot more to do with what calls to Quill.register are made internally. Behold, in quill/core.js I found:

Quill.register({
  'blots/block': Block,
  'blots/block/embed': BlockEmbed,
  //…

As it turns out, my code should actually be:

let BlockEmbed = Quill.import('blots/block/embed');

It would have saved me significant time if the API documentation for Quill.import() itself had confessed the connection with Quill.register() and ability to see what Quill.imports exist, instead of conveying the impression that it was more like the real ES module import.

Related: #2659