observed
Mirrors published as what the widget now holds, and returns whether it is a change by the user: a value that differs from what the mirror held before, and that did not happen inside a write of this wrapper's own.
Call this for every value the widget publishes, in the order it publishes them.
Return
true where the user changed the value, false both for a value this wrapper wrote through write and for one that repeats what the mirror already held.
Parameters
published
the value the widget now holds; it is mirrored whether or not the change is the user's.