[opt]
Special vertex mode. If 1 or 2 the new value will be stored in the last 25 vertices and copied from there during the next shape update. Using this parameter, script changed vertices will be kept during stretch or rotation operations. With value 2, vertices will be updated immediately, not only with the next shape update.
Remark
Notice: with any vertex updated caused by stretching or rotation of the object (e.g. building or growth) the vertices will be reset to their original defined position unless a special vertex mode is selected using the set_custom_permanent parameter.