These requirements were removed from the model because they were causing schema generation issues. 

ICAO

• Allow regional extension through specifying only a minimum set of required information
• Machine-readability: Must be highly machine-readable, requiring little human intervention to interpret correctly and maintain,  A machine-readable form can be converted into the TAC form with some reasonable rules.  Human readability is not a principal goal for this model
• Validatable: Must be validatable.  An extreme validation scenario will exceed all "standard" capabilities and require custom software, but a modicum of validation capabilities shall be included