(a) In proceedings to authorize the issuance of obligations under this subchapter, the district may make the obligations payable from and secured by the pledge of all or part of the revenue derived from the ownership or operation of the land, improvements, facilities, or other properties of the district, exclusive of revenue derived from taxation or assessments, or payable from and secured by the pledge of only revenue which may be derived from the ownership or operation of the land, improvements, facilities, or properties acquired with the proceeds of the sale of the obligations.
(b) The obligations may be issued in more than one series and at any time at which they may be required for carrying out the purposes of the district.

(c) Any pledge of revenue may reserve the right under conditions, specified in the pledge, to issue additional obligations which will be on a parity with, senior to, or subordinate to the obligations then being issued.