How might one enable multi-selection for a ComboBox object?

As seen in this example:
https://www.noesisengine.com/xamltoy/83 ... 4465dae091

the ListBox object allows for setting:
SelectionMode = Multiple

However, the ComboBox object sits higher in the object hierarchy, and does not inherit this property.

1. (Dear API devs,) Could this property be added to the ComboBox object by default?
2. Is there an example where this functionality is implemented as a work-around?

Thank you in advance.

The ComboBox control itslef doesn't look like a good candidate for allowing multi selection as it can only show 1 item in the box when closed.
Maybe what you want is to show a popup with multi-select list, and this can be done using Popup + ListBox with SelectionMode=Multiple. Can something like that work for you?