hello Steve, could you tell more about "signed a clause giving Packt the right of first refusal on my next two books". I am also with Packt and I don't see any

hello Steve, could you tell more about "signed a clause giving Packt the right of first refusal on my next two books". I am also with Packt and I don't see any clause like that in my contract :-) (I've finished 350 pages from 380 goal, my book is 90% finished). I am interested in details, what and why you had to sign smth like that? Regards, Kamil