I'm fairly sure this is illegal...
2D alerted and explained as Multi style, strong NT hand or weak 2 in any of D, H, S.
I believe it's illegal since the "weak" portion does not meet the criteria of any of BB 7C1B (i) to (iv), and is specifically excluded by note 4 of 7C1.
Just looking for confirmation.
Comments
OK the strong bid is OK by definition
(b) At most one from the following four options:
(i) One or more meanings which all show at least four cards in the suit opened, or [Fail]
(ii) One or more meanings which all show at least five cards in the same one specified suit, or [Fail]
(iii) One or more meanings which all show at least 4-4 in the same two specified suits, or [Fail]
(iv) Any combination of meanings that show either or both of
1) At least five cards in a suit, specified or not, which must not be the suit opened, and/or [Fail]
2) At least 5-4 in two suits, either or both of which may be specified or not, but both of which must not be the suit opened. [Fail]
They could play it as a weak two in clubs, hearts or diamonds if they so wish of course.
Note 4 is just added confirmation.
An easy test: if a 2-of-a-suit opening can be less-than-strong in (only) the suit opened, and can also be less-than-strong in (only) some other suit, it's never legal at level 4. (It's theoretically possible for an opening to be illegal at level 4 without failing this test, but that almost never happens with 2-level openings that people actually use, so it makes for a good quick check.)
This rule mostly excludes openings like "2!h is either a weak two in hearts or a weak two in spades", which is apparently a very effective opening in the competitions where it's used (presumably at IMPs!), due to being very difficult to defend against. It applies to this opening too, though.
EDIT: I notice you didn't specify the level of play. It's illegal at level 5, too, due to being Brown Sticker (Blue Book 9A3a): it could have ≤9 HCP, and doesn't promise 4 cards in any specific suit if weak.