"This document contains final regulations relating to the disclosure of return information under section 6103(l)(21) of the Internal Revenue Code, as enacted by the [ACA]. The regulations define certain terms and prescribe certain items of return information in addition to those items prescribed by statute that will be disclosed, upon written request, under section 6103(l)(21).... After consideration of the written comments and the information provided to the IRS by HHS, the proposed regulations under section 6103(l)(21) are adopted as revised by this final regulation."