Is there technical documentation available for Mass Transaction Manager?

I understand that MTM is a user-enabled tool, but I am having trouble getting subordinated search/validation to work. Specifically, we want to use Project and Activity as MTM criteria on an Asset Recat transaction. Ideally this means that once a BU is entered, Project is limited to that BU and once a Project is selected, Activity is limited to that BU/Project. I have no trouble using the existing delivered Views for the Project search, but the Activity search either shows all activities or none because it is searching with a Project_ID equal to blank. The Asset Subtype validation is similar,