The accessibility support here is a BIG deal! The previous versions of CodeMirror confused the heck out of screenreader applications (the way the DOM was constructed). I used CM in an open source side project which wound up getting legs, and was the horrified to learn I had built something with a reasonably large user base, that was quite inaccessible, without a great path to fix it.

I / my company (Grove Collaborative) got in touch with Marijn (the developer of CM) in 2018, asking if we could fund the project specifically to support accessibility. He very kindly shared that the next version (which appears to have been 6) was not yet under development and there was no way to put those dollars to work on that theme at that time -- but please check back in six months because he is thinking about it.

The integrity here is pretty amazing; he actually turned down the funding because the dollars couldn't, at that time, be allocated to accessibility in good faith even though he was actually preparing to do the work.

It's so SO cool to see that he was taking it seriously, and that the work got done, and I can finally update the open source project.

And, yes - accessibility should be a focus at the beginning...but if the best time to do it was years ago, the next best time is now.