Comment by hnbad

In some jurisdictions (e.g. Germany) "copyright" belongs exclusively to the author/creator and is non-transferrable, the German word for "copyright" (Urheberrecht) also literally translates to "author's right"). So instead of transferring copyright to an entity (e.g. the employer) you only grant an "exclusive, transferrable and unrestricted" license to that entity, essentially prohibiting you from using it without their permission while technically still retaining that right. This is also why CC0 exists as a substitute for a public domain declaration because in these jurisdictions it is literally impossible to transfer your copyright to the public domain.

In Germany copyright law there is actually one provision for the real transfer of copyright: death. So as far as copyright is concerned, the transfer of copyright requires literally death of the author - which might get a chuckle out of people into media studies.