Specifically, the authors of prior versions have to be acknowledged and certain ""invariant sections"" specified by the original author and dealing with his or her relationship to the subject matter may not be changed. If the material is modified, its title has to be changed (unless the prior authors give permission to retain the title). The license also has provisions for the handling of front-cover and back-cover texts of books, as well as for ""History"", ""Acknowledgements"", ""Dedications"" and ""Endorsements"" sections.