[Pharo-project] license of the collaborative book

Hi folks. I am not sure how does it work the license in the collaborative book. So far in the footer of the book I saw: "Licensed under Creative Commons BY-NC-SA" Now...what does it mean? That everybody is agree that whan he writes will be with that license? I wonder..suppose in one year we want to take such book an generate a real pdf/printed book, will be there some problem with that? I want to avoid such problems in the future. Thanks Mariano