ViewModels have a rooted AccessExpression that should return true or false (empty defaults to true). This expression controls whether the ViewModel is shown or not - the evaluation is done after any <a href="/Training:Access_control_system_in_MDriven" title="Training:Access control system in MDriven" data-bs-title="Training:Access_control_system_in_MDriven">accessgroup</a> evaluation. This expression complements the accessgroups as it checks the root objects' values and not only global values as accessgroups.

The AccessExpression can be checked before ViewModel creation with the OCL <a href="/Documentation:OCLOperators_canAccess" title="Documentation:OCLOperators canAccess" data-bs-title="Documentation:OCLOperators_canAccess">canAccess</a> operator.

Note: Prior to 2021-02-01, the AccessExpression and AccessGroup.ViewEnableExpression had issues in both WPF and Turnkey - but are now fixed.