The “middleman” in this chain of events is a COM command wrapper supplied by your application. This is a simple event wrapper based on the standard Microsoft IPropertyNotifySink interface. If your COM object wrapper was registered in the most recent call to the acedSetIUnknownForCurrentCommand() function, your COM command wrapper can be instantiated as a “listener” that receives notification from the object when one of its properties changes. Your command handler consults this COM command wrapper to determine whether it should prompt for a property, or move to the next prompt.
Figure 2 - Command-line synchronization