Related:

• Auto makers do it with standard equipment (or optional equipment).
• This product is meant for educational purposes only.
  Any resemblance to real persons, living or dead is purely coincidental....
• To IBM, 'open' means there is a modicum of interoperability among some of their equipment.
  -- Harv Masterso...
• Pain is inevitable, suffering is optional.
• RAMBO XIV....This time it's optional!
• This is an offense-optional message.
• Whips required... Chains optional...
• ...Yes, the lectures are optional. Graduation is also optional. -- Professor Brian Qui