Guidelines

A default value hook is comparable to an on set hook.

In a default value hook you must set the attribute to which the default value hook is linked. This variable is not declared in the hook code. You can only set one attribute implementation in a default value hook.

The attribute implementation’s used attributes can be used to determine the default value.

A default value hook can be used if the default value is not a constant value. For example, if it is based on used attributes or on a parameter value from the database. In other cases, a simple default value can be linked to the attribute implementation.

Note that an attribute implementation can have both a default value and a default value hook. In that case the default value hook has precedence over the default value. The default value is only used if the default value hook doesn’t overwrite its value.