Get the full text of one FDA regulation — a US Food & Drug Administration rule codified in 21 CFR — by its citation. Returns the exact regulatory wording currently in force. Answers "what does 21 CFR 211 require", "what is the FDA regulation for X", "does the FDA require X", "read 21 CFR 211.100", "the FDA good manufacturing practice rule". Forgiving citation input: "211.100", "21 CFR 211.100", "§211.100", even "211.100(a)" (paragraph stripped to the section). Covers 21 CFR part 211 current good manufacturing practice (cGMP / GMP) for finished drugs, part 210 cGMP general, part 820 quality system regulation / QMSR for medical devices, part 801 medical device labeling, part 101 food labeling / nutrition facts, part 314 new drug applications (NDA/ANDA), part 807 device establishment registration, part 111 dietary supplement cGMP, part 1308 controlled substance schedules — the whole of Title 21 (food, drugs, devices, cosmetics, biologics). This is FDA REGULATIONS (the rules/regulatory text); for FDA DATA (drug labels, adverse events, recalls) use the openfda tools. Pass a whole part (e.g. "211" or "820") to get that part's section list. Example: fda_regulation({ citation: "211.100" }) -> written procedures / process control; fda_regulation({ citation: "21 CFR 101.9" }) -> nutrition labeling. Keyless.