Johnny and Clyde are two audit staff associates working on the audit of Peabody Enterprises, a supplier of frozen foods and other frozen goofs throughout the continental United States. At lunch one day, Johnny mentions to Clyde that he overheard his supervisor discussing a voucher system with respect to audit documentation supporting the purchases payables cycle. Johnny asks Clyde to explain what exactly the voucher system is$.$ Which of the finally represents Clyde's best response to this question?