Cal. Pub. Util. Code § 100413

If bonds are authorized that contain a provision for special taxes under subdivision (i) of Section 100400, the board may enter into such convenants as may be deemed proper to provide for issuance of additional parity bonds and the priority and pledge of special taxes; and such other covenants as are customary or desirable in the issuance of any bonds payable out of special funds or as are necessary, convenient, or desirable to secure the bonds or tending to make them more marketable, subject to the provisions of the ordinance calling the bond election.