ASPxGridLookup - How to bind a lookup based on multiple selection of another lookup

This example demonstrates how to implement two cascaded ASPxGridLookup controls:
To implement it, perform the following steps:

1) Handle the server-side ASPxGridLookup.Init event of a "detail" lookup and subscribe to the CustomCallback event of a nested ASPxGridView object;
2) Handle the client-side ASPxClientGridLookup.ValueChanged event of a "master" lookup;
3) Perform a custom callback of the "detail" ASPxGridLookup via the ASPxClientGridLookup.GetGridView().PerformCallBack method;
4) Handle the "detail" ASPxGridView.CustomCallback event and define a filter expression for a "detail" datasource based on selected values of the "master" lookup;
5) Save a modified select command to the session to load it when the "detail" ASPxGridLookup/ASPxGridView is initialized after a callback.