Not as obscure as you might think – and definitely in the public interest:
Final Incorporation by Reference Rule Implements Recommendation 2011-5 (from Legal Research Plus, with links to Fed Register)
“Today, the Office of the Federal Register (OFR) published its final rule on incorporation by reference. See Incorporation by Reference, 79 Fed. Reg. 66,267 (Nov. 7, 2014). The Freedom of Information Act allows agencies to incorporate by reference into federal regulations extrinsic materials that are “reasonably available to the class of persons affected.” 5 U.S.C. § 552(a)(1). ….
OFR’s final rule is a significant step towards the implementation of Recommendation 2011-5, Incorporation by Reference. The rule emphasizes that promulgating agencies have the primary obligation to ensure that incorporated materials are reasonably available to the public. . . .
The final rule also sensibly retains the requirement that material incorporated by reference be technical in nature. This is consistent with paragraph 15 of Recommendation 2011-5, which provides that agencies should clearly establish regulatory requirements in the text of their proposed and final rules, and use incorporation by reference only to provide technical detail.”