(a) In this section, "net revenue" means the district's gross revenue less the amount necessary to pay the reasonable cost of maintaining and operating the district and the district's property.
(b) The board may issue bonds payable, as pledged by board resolution, from:
(1) all or part of the district's net revenue;
(2) the net revenue of one or more contracts made before or after the issuance of the bonds; or
(3) other revenue or income specified by board resolution or in the trust indenture.
(c) The pledge may reserve the right to issue additional bonds on a parity with, or subordinate to, the bonds being issued, subject to conditions specified by the pledge.