If binding a control using a multiple select as widget, the bound value is a text value containing a list of values to be matched against the list of option values that the select displays.
In this example the select builds a list of options from the items in the 'vars' instance. The control
itself bind to the selected node. The value of the control will determine which options become
selected.
Please note the value-prop="selectedOptions" on second control. This setting is required to map the values
correctly.
As we're using update-event="change" on the control the bound value is updated each time the user
clicks one of the items and update the input above.