1 CFR § 18.20 - Identification of subjects in agency regulations.
(a) Federal Register documents. Each agency that submits a document that is published in the Rules and Regulations section or the Proposed Rules section of the Federal Register shall—
(1) Include a list of index terms for each Code of Federal Regulations part affected by the document; and
(2) Place the list of index terms as the last item in the Supplementary Information portion of the preamble for the document.
(b) Federal Register Thesaurus. To prepare its list of index terms, each agency shall use terms contained in the Federal Register Thesaurus of Indexing Terms. Agencies may include additional terms not contained in the Thesaurus as long as the appropriate Thesaurus terms are also used. Copies of the Federal Register Thesaurus of Indexing Terms are available from the Office of the Federal Register, National Archives and Records Administration, Washington, D.C. 20408.