This excerpt taken from the PETM DEF 14A filed May 8, 2006.
Tax Withholding. The Board may require a participant to satisfy any federal, state, local, or foreign tax withholding obligation relating to a stock award by: (a) causing the participant to tender a cash payment, (b) withholding from amounts otherwise payable to the participant, (c) withholding a portion of the shares otherwise issuable to the participant, or (d) accepting delivery of other unencumbered Common Stock from the participant.
Minimum Vesting Period. Any stock awards granted under the 2006 Plan with a purchase price less than the fair market value of the Common Stock on the date of grant must have a cumulative weighted average vesting period of at least three years from the date of grant (when combined with the cumulative weighted average period for similar stock awards granted under the 2003 Plan after January 31, 2003 and before the effective date of the 2006 Plan). However, stock awards vesting on an accelerated basis pursuant to performance criteria, a corporate transaction or change in control (as described below), or the Executive Change in Control and Severance Benefit Plan, are not taken into account for purposes of this limitation.
Automatic Exercise of Expiring Stock Awards. The Board may issue stock options or stock appreciation rights that provide that in the event of a pending expiration or termination of such stock option or stock appreciation right, we may issue to the affected participant (in cash or Common Stock) the excess of: (a) the aggregate fair market value of Common Stock that the participant would have received upon exercise of such option or stock appreciation right, over (b) the aggregate exercise price in effect for those shares.