A constraint Block is a subtype of a Block. It is a class stereotyped with «ConstraintBlock». It has a constraint with an expression to constrain the values of its constraint parameters. If an object initialized from a constraint Block and a value bound to a constraint parameter of that object is changed, Magic Model Analyst / Cameo Simulation Toolkit will evaluate the expression of the constraint. You can see more information about how Magic Model Analyst / Cameo Simulation Toolkit evaluates an expression in Evaluating expressions.