Wis. Stat. § 229.56: Funding and refunding bonds.

(1) A district may issue bonds to fund or refund any outstanding bond, including the payment of any redemption premium on the outstanding bond and any interest accrued or to accrue to the earliest or any subsequent date of redemption, purchase or maturity.

(2) A district may apply the proceeds of the bonds issued to fund or refund any outstanding bond to the purchase or retirement at maturity or redemption of the outstanding bond either on its earliest or any subsequent redemption date or upon the purchase or at the maturity of the bond. A district may, pending application, place the proceeds in escrow to be applied to the purchase or retirement at maturity or redemption on any date the board of directors determines.