Implementation within the Custom HTML tag remains the same.
To implement a dropdown menu, the controlled object needs a list property of type array. Example:
var model = {
tests: {
list: [ {text: 'test1', value: 100, selected:true}, {text: 'test2', value: 1000} ]
}
}
The list array can be empty but it must be present. Then the options can be set in Custom HTML tag as before.