CowBall

I'm proposing a solution here! (for programmers only) https://www.drupal.org/project/diff_different https://www.drupal.org/project/diffadvance In drupal CMS, using these 2 modules together can diff html by highlighting the difference instead of diffing the plaintext. I'm not sure how evernote stores notes but it should be something similar. For end users, we can install drupal with these 2 modules to check the conflicts. For evernote developers, they can download the source code of these 2 modules and make use of it.