I have just enabled local modifications to permit visual (“rich text”) editing of comments on posts. Since 2018-02-15 users have been able to edit their own comments on posts. However, editing was always with the “Quicktags” editor, in which the user edits the HTML code of the comment, not the visual presentation used by default when composing a comment (using the “TinyMCE” editor).
The change makes the TinyMCE visual editor available, and the default, when editing comments. The Quicktags editor remains available for those who prefer it, or when editing the comment at the HTML level is the only way to accomplish what you’re trying to do (for example, custom styles, fonts, colours, etc.). The “Add Media” button is available when in Visual mode, making it easy to add new images while editing comments. Shortcodes, such as those for spoilers, mathematics, and drop capitals, may be used in either Visual or Text mode editing.
This is actually, in terms of lines of code, a relatively minor change, but developing it required extensive research into how WordPress handles editing comments, culminating in a marathon session described in the Updates group post for 2018-05-03. But given the towering and tottering stack of hacks which is WordPress, the consequences of even the smallest change can be profound, so since putting the new code into production today, 2018-05-04 at 19:30 UTC, I have been watching the HTTP error_log closely for any errors. If you notice any strange behaviour when editing comments in either Visual or Text mode, please report them in comments to this post or in the Bug Reports group.
If you want to experiment with the new comment editing code or try to break it with torture tests, please use the Sand Box post, which exists for that purpose.