Factoring on the `value` test is attractive since it appeared twice (in the previous `setProperty`), but I think it hides what's happening here.

In the inner loop, we need to determine two things after calling the driver: was the action handled, and what is the result?

There are two _handled_ conditions and they are distinct. Delegation is detected regardless of the value returned. Then if delegation didn't occur, assignment is detected if a value was returned. They never intersect, and assignment can't be determined until delegation is ruled out.

    if ( _assignment counter ticked_ ) {
        delegated = true;
    } else if ( _have value_ ) {
        _tick the assignment counter_
        assigned = true;
    }

The value is promoted to the result if the action was handled. However, if the driver doesn't provide a value, the incoming value is retained so that assignments at least evaluate to the value assigned (as with `set: that.m( value )`, and many other constructions).

    if ( delegated || assigned ) {
        if ( _have value_ ) {
            _result_ = _value_
        }
    } 

If we test `value` before we know the _handled_ situation, then we don't really know anything conclusively. The value feeds into the result, but it only offers partial information about the _handled_ condition. Delegation may happen with or without a value, so that's calculated separately. Then, while setting the result, we have to consider delegation again to exclude it before we can know if assignment occurred.

It seems much clear to just do: Delegated? Assigned? Result.

The result condition is actually simpler than above. Since `_have value_` => `delegated || assigned` (because non-delegated actions returning a value are recognized as assigned), this reduces to:

    if ( _have value_ ) {
        _result_ = _value_
    }

Dropping the `delegated || assigned` makes things less clear, but it's pointless to compute it if it doesn't do anything. A better comment should cover it though.