We’re currently debating moving our text editing over to ProseMirror at work. Something we’ve missed in PM as it stands is noting / commenting. Because of this we’ve built a plugin that adds this functionality (at least to suit our requirements). It’s definitely “beta” in it’s scope / design / architecture at the moment but it seems to be serving our needs quite well. Feel free to have a play around, comment or even a PR! There are most likely areas that don’t make sense or miss part of the PM API so flag anything that makes no sense.