Which section are you buying? See the FAQ for this forum, which states:
8) What do Mandatory and Voluntary mean?
a. If a resort is Staroption "Mandatory," it means that when the week is sold to a new owner (resale) the Staroption value of the week transfers to the new owner, and the new owner has the right to exchange his timeshare in the Starwood Vacation Network. These resorts are Staroption Mandatory:
* Harborside at Atlantis
* Vistana Villages (except Amelia & St. Augustine)
* Westin St. John (except Bay Vista)
* Westin Ka'anapali & Westin Ka'anapali-North
* Westin Kierland Villas
b. If a resort is Staroption "Voluntary," it means that the Staroption value of the week DOES NOT transfer to the new owner when it is resold, and the new owner DOES NOT have the right to exchange his timeshare in the Starwood Vacation Network.