The At a Glance about SSAE No. 21, Direct Examination Engagements, explains
That the AICPA Auditing Standards Board issued SSAE No. 21 to add new AT-C section 206, Direct Examination Engagements, to the attestation standards in AICPA Professional Standards to enable practitioners to perform an examination engagement in which the practitioner obtains reasonable assurance by measuring or evaluating underlying subject matter against criteria and expressing an opinion that conveys the results of that measurement or evaluation.
How AT-C