[csande17]

I'm not aware of any actual real-world GUI system where ".whenChanged do" is valid syntax, but just for the sake of argument, pretend that it only fires when the user changes the textbox. Coincidentally, this also happens to be how the "change" event works in JavaScript.

[Izkata]

I know of one that's essentially like that [0], but like you suggested - it only fires on user action, not programmatic update.

(The examples here are for buttons and sliders, but it's the same syntax for input fields)

[0] http://rebol.com/docs/easy-vid.html#section-20