Final Answer:
Passenger restrictions for a holder of a GDL special learner or examination permit under the age of 21 typically limit the driver to having only one passenger, unless accompanied by a parent or guardian.
Step-by-step explanation:
In many jurisdictions, Graduated Driver Licensing (GDL) systems impose restrictions on young drivers with special learner or examination permits. For those under 21, the common restriction is allowing only one passenger in the vehicle, unless accompanied by a parent or guardian. This measure aims to enhance road safety by minimizing distractions and promoting responsible driving habits during the early stages of a new driver's experience. It provides a controlled environment for skill development and risk reduction.