Revenue bonds may be issued hereunder for the purpose of refunding any obligations issued hereunder. Such refunding bonds may be combined with bonds issued under the provisions of Section 3 of this act¹ into a single issue. When bonds are issued under this section for refunding purposes, such bonds may either be sold or delivered in exchange for the outstanding obligations. If sold, the proceeds may be either applied to the payment of the obligations refunded or deposited in escrow for the retirement thereof. All bonds issued under this section shall in all respects be authorized, issued, and secured in the manner provided for other bonds issued under this act and shall have all the attributes of such bonds. The resolution under which such refunding bonds are issued may provide that any of the said refunding bonds shall have the same priority of lien on the revenues pledged for their payment as was enjoyed by the obligations refunded thereby.