[belorn]

Many legal concepts used by courts has no legal recognition in the law texts. Much of legal practice are just precedents, policies, customs, and doctrines.

Parent comment mention music synchronization rights, and this concept does not exist in copyright. Court do occasionally mention it, and lawyers talks about it, but in terms of the legal recognition there is basically only the law text that define derivative work and fair use. One way to interpret it is that court has precedents to treat music synchronization as a derivative work that do not fall under fair use.

Using textbooks in training/education is not as black and white that one may assume. Take this Berkeley (https://teaching.berkeley.edu/resources/course-design/using-...). Copying in this context include using pages for slides and during lectures (which is a slightly large scope than making physical copies on physical paper). In obvious case the answer is likely obvious, but in others it will be more complex.