> The same operation used to require implementing a single delegate method in 1990s AppKit.
I find that hard to believe.
And not to "uhm, ackshually" you, but what you're describing is possible via the native HTML "contenteditable" property.
https://developer.mozilla.org/en-US/docs/Web/HTML/Global_att...
(Actually doing something useful with edits is another story, but that's not what the comment is about)