Exchanging information between Event Handlers
An Event Handler has access to a shared pool of key-value pairs called context variables that can be used to find out more about other Event Handlers in the system.
The key-value pairs can be retrieved from the ContextVariables property of the TcmEventArgs class in the Tridion.ContentManager.Extensibility namespace.
An Event Handler can also add key-value pairs to this property provided the key used is unique.
You can find an example of the use of the ContextVariables property in Event Handler example.