The use of special purpose behaviors is optional. If they are missing for a component, the corresponding behaviors of all subcomponents of the component are called recursively. If a special purpose behavior is specified however, it is responsible for explicitly calling the subcomponents. This is easily done using the composition keyword as shown in Example 2.18:

behavior reset(int level)
{
   // reset subcomponents
   composition.reset(level);
   // reset state variables
   status = 0;
   counter = 0;
   control = 0;
}

A missing special purpose behavior B is equivalent to:

behavior B
{
   composition.B();
}