Gov. Code, § 67585

Refunding bonds may be issued in a principal amount sufficient to provide funds for the payment of all bonds to be refunded thereby, and in addition for the payment of all expenses incident to the calling, retiring or paying of such outstanding bonds, and the issuance of such refunding bonds. These expenses may include the difference in amount between the par value of the refunding bonds and any amount less than par for which the refunding bonds are sold, any amount necessary to be made available for the payment of interest upon such refunding bonds from the date of sale thereof to the date of payment of the bonds to be refunded or to the date upon which the bonds to be refunded will be paid pursuant to the call thereof or agreement with the holders thereof, and the premium, if any, necessary to be paid in order to call or retire the outstanding bonds and the interest accruing thereon to the date of the call or retirement.