Please add a trigger to the Filter widget so that other widgets can be notified when a filter is added/removed/altered. Ideally the generated message would contain the same SQL string which is used for the "where" property in the updateQueryParams method.
I have custom widgets which need to respond to filter changes. This enhancement would allow an Experience author to "wire together" the out-of-the-box Filter widget and the custom widgets in the Builder environment without having to resort to custom programming.