Compare eCFR regulation text across two dates to detect rule changes affecting a compliance workflow

Steps

1. No API key is required; retrieve the full structure of a title: GET https://www.ecfr.gov/api/versioner/v1/structure/{date}/title-{n}.json where date is YYYY-MM-DD and n is the CFR title number
2. Fetch the XML content of a specific section as of a date: GET https://www.ecfr.gov/api/versioner/v1/full/{date}/title-{n}.xml?section={part}.{section} — returns the full XML text of the section as it existed on that date
3. Fetch the same section for a second date and diff the two XML strings (stripping XML tags) to identify changed regulatory language
4. Use the ancestry endpoint for efficient navigation: GET https://www.ecfr.gov/api/versioner/v1/ancestry/{date}/title-{n}.json?part={part}&section={part}.{section} to confirm the section existed on both dates
5. To enumerate all dates on which a section changed, call GET https://www.ecfr.gov/api/versioner/v1/versions/title-{n}.json and filter by part to find all amendment dates
6. Retrieve the associated Federal Register document for each amendment date from the FR doc link embedded in the version metadata to get the preamble explanation of the change