3.2.28 The ITT shall be published in GeBIZ. GPEs should use output/ outcome-based performance specifications as much as possible in its PPP contracts, although some input-based specifications may be necessary for certain requirements of the GPE in the PPP contract. Output specifications will allow the potential bidders as much as flexibility as possible to produce innovative proposals as well as not to restrict the GPE from considering alternative proposals. GPEs should also include a clause on periodic market testing in the tender. This is to ensure that the unitary payment is a fair and viable one.