All bonds issued by any board, and the appropriate proceedings authorizing their issuance, shall be submitted to the Attorney General of the State of Texas for examination. If he finds that such bonds have been authorized in accordance with law he shall approve them, and thereupon they shall be registered by the comptroller; and after such approval and registration such bonds shall be incontestable in any court, or other forum, for any reason, and shall be valid and binding obligations in accordance with their terms for all purposes.