Sub parameter expression rules control when parameters are visible or hidden. These rules work like sub parameter rules with the difference that the trigger is a Boolean expression which allows more complex logic.

Definition of trigger and parameters to show/hide

A sub parameter expression rule contains a trigger and one or more parameters whose visibility shall be controlled.

The trigger expression is a Boolean expression, and the rule is triggered as long as the expression is true. An empty trigger expression is treated as always true.

The parameters whose visibility shall be controlled by a sub parameter expression rules are selected in the list of sub parameters. Selected parameters become visible when the rule's triggering condition is met. If many sub parameter rules or sub parameter expression rules affect the same parameter, it's enough that one of these rules' triggering conditions are met for the parameter to become visible.

Parameters that always shall be hidden

By creating a sub parameter expression rule with false as trigger expression those parameters that are selected as sub parameters will always be hidden, unless they are made visible by another sub parameter rule or sub parameter expression rule.  This can for example be used when introducing new parameters that should not yet be possible to set but are needed for the preparation of other parts of the configuration model like prices, bill of materials or visualizations. By also setting the site effectivity for the rule the new parameters can be made available for testing in the administration site meanwhile being hidden in the production site.

Hidden parameters are disabled

A parameter that is hidden via sub parameter expression rules is also disabled. This means that the parameter is not an effective part of the configuration model, it gets the default value of its data type during execution of expressions and will not get a saved value even if the user had set a value before the parameter was hidden. Notice the difference compared to a parameter on a hidden tab which can still have a value even though the parameter is not visible to the user.

Restoring the value when reappearing

If a parameter that has been set to a value becomes hidden and later is shown again during the same editing session, then the system will try to restore its previous value. However, if this value is no longer allowed due to rules the value of the parameter is cleared out.