sometimes clauses are implicit in the law or collective contracts or come from case law so on the contract you sign you don't have to specify it, contracts are still bound by law and law takes precedence most of the time and ultimately you have to read the whole thing to know what a contract actually bounds you to in it's entirety, which is way you resolve disputes you need a specialist

Italy for example has a blanket "we own everything" statement on the standard collective contract, and to work around that you need to write an agreement and sign it on the side (not on the main contract) or it won't stick in court because all clause against the collective contract are considered vexatious by default and require special care