The general rules of interpretation, section, chapter, and subheading notes (including those labeled “Additional U.S. Notes”), and the terms of the headings and subheadings constitute the legal text of the HTS. The titles of sections, chapters and subchapters are provided for ease of reference only and have no legal significance. Similarly, endnotes referring to other HTS codes (for example, “See 9903.88.01”) are provided for ease of reference and have no legal significance. You may also notice additional documents such as the China Tariff Guidance document here (PDF). As with the endnotes, these documents are provided for ease of reference and are not part of the legal text of the HTS. 

Statistical Reporting Numbers are not legal but are important in gathering trade data. The 10-digit number for each imported good (its 8-digit subheading plus the statistical suffix) must be used on entries.  However, the stat suffixes, the statistical-level descriptions, and the units of quantity are administratively adopted rather than being enacted.  See the second part of the Preface to each annual or Basic Edition of the HTS for more information.