How to Invoke Custom API Query for MultiSelectDialog?

Documentation for MultiSelectDialog “get_query” states:
“A function that returns query and filters to query the selection list. A custom server side method can be passed via query , and filters will be passed to that method.

However, none of the examples on the page demonstrate invoking a custom server side method. Moreover, I looked at multi_select_dialog.js to try to see if the code even supports the feature, and it looks like it does not support it.

Is the documentation wrong? Am I interpreting it wrong? Is it actually supported and just not demonstrated?