[26] Dictionary definitions of the noun "period" do not, in my view, resolve the construction question, because s 15(b) of the Dangerous Prisoners (Sexual Offenders) Act 2003 contemplates a "period" with a further qualification: that it is capable of being "stated". I do not think one can "state" a period other than by identifying its duration. There is, also, what I consider to be the telling point made by Mr Moynihan for the appellant: that if the legislature had wished to enable imposition of supervision orders for indefinite periods, it could readily have done so by saying as much; as, indeed, it did in respect of continuing detention orders, which, pursuant to s 13(5)(a), are to be "for an indefinite term". That distinction between the detention order and supervision order regimes is further illustrated by these features: continuing detention orders must be reviewed annually (s 27) and, if, on such a review the court is not satisfied the prisoner continues to pose a serious danger, must be rescinded (s 30(5)); in sharp contrast with supervision orders, in respect of which there is no review mechanism, nor provision for their rescission if they are no longer needed. That absence of review suggests that it is when a supervision order is made that the court must attempt to establish the duration for which it is likely to be needed.