Justice Scalia on a key difference between Statute and Regulation in American law : "When Congress enacts an imprecise statute that it commits to the implementation of an executive agency, it has no control over that implementation (except, of course, through further, more precise, legislation). The legislative and executive functions are not combined. But when an agency promulgates an imprecise rule, it leaves to itself the implementation of that rule, and thus the initial determination of the rule’s meaning. And though the adoption of a rule is an exercise of the executive rather than the legislative power, a properly adopted rule has fully the effect of law. It seems contrary to fundamental principles of separation of powers to permit the person who promulgates a law to interpret it as well."
In software terms, I think of it this way: if you write an API, make sure somebody else implements it as well as you. Your API will be that much better for it. True meaning is the result of independent interpretation.